Short Trick to convert given ratio into required ratio

Duration: 8 min

This video lesson is available to enrolled students.

Return to /learn/UPESSC-ASSISTANT-TEACHER-RECRUITMENT/mathematics-practice/averages-ages-mixtures-1di6ctl/ratio-division-of-quantities-rm3i9w/asset-short-trick-to-convert-given-ratio-into-required-ratio after enrolling

Inside: a video lesson and guided study material.

Module outline

  1. हिंदी / Hindi — भाषा खंड: भाषा, लिपि और वर्ण-विचार, संधि, शब्द-स्रोत और शब्द-रचना, समास, शब्द-भेद: विकारी और अविकारी, लिंग, वचन, कारक, काल और वाच्य, वाक्य-विचार और शुद्ध लेखन, शब्द-भंडार, रस, छंद, अलंकार और शब्द-शक्ति, अपठित बोध, हिंदी शिक्षणशास्त्र
  2. संस्कृत / Sanskrit — भाषा खंड: वर्णविचारः एवं संज्ञाप्रकरणम्, सन्धिप्रकरणम्, शब्दरूपाणि, धातुरूपाणि, कारकाणि एवं विभक्तयः, उपसर्गाः एवं अव्ययानि, प्रत्ययप्रकरणम्, समासप्रकरणम्, वाच्यप्रकरणम्, संख्याज्ञानम्, शब्दज्ञानम् एवं अनुवादः, अपठितावबोधनम्
  3. English — Language Section: Sounds, Spelling and Word Formation, Parts of Speech, Nouns and Pronouns, Articles, Determiners and Adjectives, Verbs and Modals, Tenses and Subject–Verb Agreement, Adverbs, Prepositions and Conjunctions, Sentence Structure, Voice and Narration, Vocabulary, Sentence Correction and Writing Skills, Poetry and English Literature, Reading Comprehension, Pedagogy of English Language
  4. GK & Current Affairs / सामान्य ज्ञान एवं समसामयिक घटनाएँ — 25 Questions: Indian Economy: Data & Current Affairs / भारतीय अर्थव्यवस्था: आँकड़े एवं समसामयिकी, Indian Art & Culture / भारतीय कला एवं संस्कृति, Science & Technology / विज्ञान एवं प्रौद्योगिकी, Environment & Climate Affairs / पर्यावरण एवं जलवायु समसामयिकी, Defence & Security / रक्षा एवं सुरक्षा, Static General Knowledge / स्थिर सामान्य ज्ञान, Awards & Honours / पुरस्कार एवं सम्मान, Sports / खेल जगत, Government Schemes, Governance & Infrastructure / सरकारी योजनाएँ, शासन एवं आधारभूत संरचना, International Relations & Organisations / अंतरराष्ट्रीय संबंध एवं संगठन, Key Appointments & Office Holders / प्रमुख नियुक्तियाँ एवं पदधारक, Uttar Pradesh GK / उत्तर प्रदेश सामान्य ज्ञान
  5. Mathematics / गणित — 16 Questions: Number System & Place Value / संख्या पद्धति एवं स्थानीय मान, Basic Operations, Simplification & Patterns / मूलभूत संक्रियाएँ, सरलीकरण एवं पैटर्न, Factors, Divisibility, HCF & LCM / गुणनखंड, विभाज्यता, म.स.प. एवं ल.स.प., Fractions & Decimals / भिन्न एवं दशमलव, Squares, Cubes, Exponents & Surds / वर्ग, घन, घातांक एवं करणी, Measurement: Length, Mass, Capacity, Time & Money / मापन: लंबाई, भार, धारिता, समय एवं मुद्रा, Algebra / बीजगणित, Ratio, Proportion, Average & Ages / अनुपात, समानुपात, औसत एवं आयु, Percentage, Profit–Loss & Interest / प्रतिशत, लाभ-हानि एवं ब्याज, Time & Work and Speed–Distance / समय-कार्य एवं चाल-दूरी, Lines, Angles, Shapes & Coordinates / रेखाएँ, कोण, आकृतियाँ एवं निर्देशांक, Triangles, Quadrilaterals, Circles & Trigonometry / त्रिभुज, चतुर्भुज, वृत्त एवं त्रिकोणमिति, Mensuration: Perimeter, Area & Volume / क्षेत्रमिति: परिमाप, क्षेत्रफल एवं आयतन, Data Handling, Statistics & Probability / आँकड़ा प्रबंधन, सांख्यिकी एवं प्रायिकता, Mathematics Pedagogy / गणित शिक्षणशास्त्र
  6. Science / विज्ञान — 8 Questions: Technology, Measurement and Motion / प्रौद्योगिकी, मापन एवं गति, Force, Pressure, Work and Energy / बल, दाब, कार्य एवं ऊर्जा, Heat and Sound / ऊष्मा एवं ध्वनि, Light / प्रकाश, Electricity and Magnetism / विद्युत एवं चुंबकत्व, Universe and Natural Phenomena / ब्रह्मांड एवं प्राकृतिक परिघटनाएँ, Matter and Its Structure / पदार्थ एवं उसकी संरचना, Chemical Reactions, Acids, Bases and Salts / रासायनिक अभिक्रियाएँ, अम्ल, क्षार एवं लवण, Metals, Non-metals and Materials of Daily Use / धातु, अधातु एवं दैनिक उपयोग की सामग्री, Living World: Classification, Cell and Tissues / सजीव जगत: वर्गीकरण, कोशिका एवं ऊतक, Plants: Nutrition, Transport and Reproduction / पादपों में पोषण, परिवहन एवं जनन, Human Body and Organ Systems / मानव शरीर एवं अंग तंत्र, Food, Nutrition and Health / भोजन, पोषण एवं स्वास्थ्य, Environment and Ecology / पर्यावरण एवं पारिस्थितिकी, Science Pedagogy / विज्ञान शिक्षण शास्त्र
  7. Environment & Social Studies / पर्यावरण एवं सामाजिक अध्ययन — 8 Questions: Ancient Indian History / प्राचीन भारत का इतिहास, Medieval Indian History / मध्यकालीन भारत का इतिहास, Colonial India and Social Reform / औपनिवेशिक भारत एवं समाज सुधार, Indian National Movement and Independent India / भारतीय राष्ट्रीय आंदोलन एवं स्वतंत्र भारत, Earth, Globe and Maps / पृथ्वी, ग्लोब एवं मानचित्र, Physical Geography / भौतिक भूगोल, Natural Vegetation, Wildlife and World Regions / प्राकृतिक वनस्पति, वन्य जीवन एवं विश्व के प्रदेश, Geography of India / भारत का भूगोल, Resources and Development / संसाधन एवं विकास, Social and Political Life / सामाजिक एवं राजनीतिक जीवन, Indian Constitution / भारतीय संविधान, Government: Union, State and Local / सरकार: केंद्र, राज्य एवं स्थानीय, Economics and Indian Economy / अर्थशास्त्र एवं भारतीय अर्थव्यवस्था, Social Science Pedagogy / सामाजिक विज्ञान शिक्षणशास्त्र, Family, Friends and Community / परिवार, मित्र और समुदाय, Plants / पौधे, Animals / जंतु, Farming and Animal Husbandry / खेती और पशुपालन, Food and Nutrition / भोजन और पोषण, Body and Health / शरीर और स्वास्थ्य, Water / जल, Shelter / आवास, Travel, Transport and Communication / यात्रा, परिवहन और संचार, Maps, Directions and India / मानचित्र, दिशाएँ और भारत, Things We Make and Do / हम क्या बनाते और करते हैं, Earth, Sky and Disasters / पृथ्वी, आकाश और आपदाएँ, Environment, Ecology and Wildlife / पर्यावरण, पारिस्थितिकी और वन्यजीव, Natural Resources, Pollution and Climate Change / प्राकृतिक संसाधन, प्रदूषण और जलवायु परिवर्तन, Pedagogy of Environmental Studies / पर्यावरण अध्ययन का शिक्षणशास्त्र
  8. Teaching Skills / शिक्षण कौशल — 8 Questions: Curriculum and School Activities / पाठ्यचर्या और विद्यालयी गतिविधियाँ, Lesson Planning and Teaching Skills / पाठ योजना और शिक्षण कौशल, Teaching Resources and Educational Technology / शिक्षण संसाधन और शैक्षिक प्रौद्योगिकी, Classroom Management and Communication / कक्षा प्रबंधन और सम्प्रेषण, School Leadership and Administration / विद्यालय नेतृत्व और प्रशासन, Constitution, Commissions, Acts and Schemes in Education / संविधान, आयोग, अधिनियम एवं योजनाएँ
  9. Child Psychology / बाल मनोविज्ञान — 8 Questions: Concept of Development / विकास की अवधारणा, Psychological Theories of Development / विकास के मनोवैज्ञानिक सिद्धांत, Individual Differences, Personality and Gender / व्यक्तिगत भिन्नताएँ, व्यक्तित्व एवं जेंडर, Intelligence and Creativity / बुद्धि एवं सृजनात्मकता, Learning and Its Theories / अधिगम एवं इसके सिद्धांत, How Children Think and Learn / बालक कैसे सोचते एवं सीखते हैं, Emotion, Motivation, Mental Health and Guidance / संवेग, अभिप्रेरणा, मानसिक स्वास्थ्य एवं निर्देशन, Inclusive Education / समावेशी शिक्षा, Teaching-Learning Process / शिक्षण-अधिगम प्रक्रिया, Teaching Methods and Strategies / शिक्षण विधियाँ एवं रणनीतियाँ, Assessment and Evaluation / आकलन एवं मूल्यांकन, Educational Thinkers, Aims and National Policies / शैक्षिक विचारक, उद्देश्य एवं राष्ट्रीय नीतियाँ
  10. Life Skills, Management & Attitude / जीवन कौशल, प्रबन्धन एवं अभिवृत्ति — 8 Questions: Teacher Identity and Professional Development / शिक्षक पहचान और व्यावसायिक विकास, Life Skills, Values, Peace and Environmental Education / जीवन कौशल, मूल्य, शांति एवं पर्यावरण शिक्षा
  11. Logical Reasoning / तार्किक ज्ञान — 5 Questions: Alphabet & Number Test / वर्णमाला एवं संख्या परीक्षण, Series / श्रृंखला, Analogy & Classification / सादृश्यता एवं वर्गीकरण, Coding-Decoding / कूटलेखन एवं कूटवाचन, Mathematical Operations & Arithmetical Reasoning / गणितीय संक्रियाएँ एवं अंकगणितीय तर्क, Blood Relations / रक्त संबंध, Direction & Distance / दिशा एवं दूरी, Ranking, Seating Arrangement & Puzzles / क्रम, बैठक व्यवस्था एवं पहेली, Calendar & Clock / कैलेंडर एवं घड़ी, Venn Diagrams & Logical Deduction / वेन आरेख एवं तार्किक निगमन, Statement-Based Reasoning / कथन आधारित तर्क, Non-Verbal Reasoning / अशाब्दिक तर्क, Dice & Cubes / पासा एवं घन
  12. Information Technology / सूचना तकनीकी — 4 Questions: Introduction to Computers / कंप्यूटर का परिचय, Computer Hardware and Peripherals / कंप्यूटर हार्डवेयर एवं परिधीय उपकरण, Computer Memory / कंप्यूटर मेमोरी, Number System and Data Representation / संख्या पद्धति एवं डेटा निरूपण, Software and Programming Languages / सॉफ्टवेयर एवं प्रोग्रामिंग भाषाएँ, Operating System / ऑपरेटिंग सिस्टम, MS Office / एमएस ऑफिस, Database Management System (DBMS) / डेटाबेस प्रबंधन प्रणाली (DBMS), Computer Networks / कंप्यूटर नेटवर्क, Internet and its Services / इंटरनेट एवं उसकी सेवाएँ, Cyber Security / साइबर सुरक्षा, Digital Society, IT Act and E-Governance / डिजिटल समाज, आईटी अधिनियम एवं ई-गवर्नेंस, Emerging Technologies / उभरती तकनीकें, ICT in Education / शिक्षा में ICT
  13. अतिरिक्त अभ्यास (वैकल्पिक) / Extra Practice — beyond the 2026 syllabus: World History and International Relations / विश्व इतिहास एवं अंतरराष्ट्रीय संबंध, संस्कृतसाहित्यम् एवं काव्यशास्त्रम्, संस्कृतशिक्षणशास्त्रम्, हिंदी साहित्य
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture by Yash Jain teaches a shortcut for ratio and proportion problems asking what number must be added to or subtracted from each term of a given ratio a:b so that it becomes c:d. The lesson begins by defining a ratio as a comparison of two quantities and posing the general question: what should be added or subtracted to each term of a:b to convert it into c:d? The instructor first demonstrates the standard algebraic method using two examples. For subtraction, he solves what should be subtracted from each term of 15:19 to make it 3:4 by setting up (15-y)/(19-y) = 3/4, cross-multiplying to get 4(15-y) = 3(19-y), expanding to 60 - 4y = 57 - 3y, and solving for y. For addition, he solves what should be added to each term of 9:16 to make it 2:3 by setting up (9+y)/(16+y) = 2/3, cross-multiplying to get 3(9+y) = 2(16+y), expanding to 27 + 3y = 32 + 2y, and solving to find y = 5. The core of the lesson is then a direct shortcut formula that avoids solving equations entirely. The instructor introduces the general formula |ad - bc| / |(a+c) - (b+d)|, then simplifies the denominator to |a-c| (or equivalently the difference of the target ratio terms). The method is: cross-multiply the original and target ratios, subtract the two products to get a numerator difference, then divide by the absolute difference of the target ratio terms. Applying this to 9:16 becoming 2:3, he calculates 9*3 = 27 and 16*2 = 32, subtracts to get 5, divides by 3-2 = 1, yielding the answer 5. He notes this saves time compared to algebra, referencing a timer showing 40 seconds crossed out and replaced with 60 seconds. The lesson concludes with two practice examples: adding to 11:21 to get 3:5 (calculating 11*5 = 55, 21*3 = 63, difference 8, divided by 5-3 = 2 to get answer 4), and subtracting from 23:38 to get 4:7 (calculating 23*7 = 161, 38*4 = 152, difference 9, divided by 7-4 = 3 to get answer 3). The consistent rule is: cross-multiply, subtract products, divide by the difference of target ratio terms.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The opening slide displays the heading 'RATIO & PROPORTION - BY YASH JAIN' with a whiteboard panel reading 'Ratio a comparison of 2 quantities' illustrated with colored dots labeled part, whole and total. A pink slide poses the general question 'What should be added/subtracted to each term of a:b to convert them to c:d?' At 35s an orange slide introduces the first specific example: 'Que: What should be added to each term of 9 : 16 so that new ratio becomes 2 : 3?' The instructor writes the fraction 9/16 with an arrow pointing to 2/3, then sets up (9+y)/(16+y) = 2/3 and cross-multiplies to '3(9+y) = 2(16+y)', expanding to '27+3y = 32+2y' and solving to get y = 5.

  2. 2:00 – 5:00 02:00-05:00

    The instructor first solves a subtraction problem for the ratio 15:19 to become 3:4 by setting up (15-y)/(19-y) = 3/4 and cross-multiplying to get 4(15-y) = 3(19-y), expanding to 60 - 4y = 57 - 3y. He then transitions back to the addition problem for 9:16 becoming 2:3 and introduces a general shortcut formula using absolute values of cross-products: |ad-bc| / |(a+c)-(b+d)|. He simplifies the denominator to |a-c|, highlighting it with a red circle. Applying the shortcut, he calculates 9*3 = 27 and 16*2 = 32, subtracts to get 5, and divides by the difference of target ratio terms (3-2 = 1), writing the final answer 5/1 on the board. A timer drawn on the board shows '40 sec' crossed out and replaced with '60 sec', indicating a time-saving goal.

  3. 5:00 – 7:54 05:00-07:54

    The instructor applies the shortcut to two additional practice problems. For 'What should be added to each term of 11 : 21 so that new ratio becomes 3 : 5?', he calculates 11*5 = 55 and 21*3 = 63, finds the difference 63-55 = 8, and divides by 5-3 = 2 to get the answer 4. For 'What should be subtracted from each term of 23 : 38 so that new ratio becomes 4 : 7?', he calculates 23*7 = 161 and 38*4 = 152, finds the difference 161-152 = 9, and divides by 7-4 = 3 to get the answer 3. The consistent method is cross-multiplying original and target ratio terms, subtracting the products, and dividing by the difference of the new ratio terms.

The central teaching point is a direct shortcut formula for converting one ratio to another by adding or subtracting the same number from each term. The standard algebraic approach sets up (a±y)/(b±y) = c/d and solves for y through cross-multiplication. The shortcut bypasses this by computing |ad - bc| divided by the absolute difference of the target ratio terms. The numerator comes from cross-multiplying the original ratio's first term with the target's second term and vice versa, then subtracting. The denominator is simply the difference between the two terms of the target ratio. This works for both addition and subtraction problems, as demonstrated with 9:16 to 2:3 (answer 5), 15:19 to 3:4, 11:21 to 3:5 (answer 4), and 23:38 to 4:7 (answer 3). The instructor emphasizes time efficiency, noting the shortcut saves significant calculation steps compared to full algebraic solving.

Loading lesson…