Mixture & Alligation IBPS PYQs

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An AI-generated summary of this video lecture.

The video is a bilingual (English/Hindi) IBPS previous-year question session on Mixture and Alligation. It opens with a title slide, then introduces the average-rate formula using 20 kg at Rs.40/kg and 30 kg at Rs.50/kg, giving (20×40 + 30×50)/(20+30) = 2300/50 = Rs.46/kg as the mixture’s cost price per kg. The instructor then solves several milk-water PYQs: (1) an 80 g mixture that is 60% milk, from which 20 g is removed and 6 g water added; initial milk = (60×80)/100 = 48 g and water = 32 g; removing one-quarter leaves 12 g milk removed, so final milk = 48−12 = 36 g and water = 32−8+6 = 30 g, ratio 36:30 = 6:5. (2) A 95 L mixture in ratio 15:4, with X litres removed and 18 L water added to give new ratio 3:2; scaling gives milk = 75, water = 20 (unit = 95/19 = 5 L); the equation 75k/(20k+18) = 3/2 is set up, and a shortcut using the final milk fraction (0.6 → 40% water) yields X = 95×40/100 = 38 L (option E). (3) A vessel where water is 25% of milk, so milk:water = 4n:n; after removing 10 L (8 L milk, 2 L water) and adding 25 L milk, the equation 4n+17 = 5(n−2) gives n = 27, total mixture = 5n+15 = 150 L (options listed around 102–116 L; exact final answer not fully visible). (4) A container in ratio 3:2, after removing 75% and adding 40 L of a 40%-milk mixture, milk becomes 44 4/9% of the result; this is introduced but not fully solved in sampled frames. (5) A problem with mixture A ratio 9:5 and related quantities, where red notes approximate decimals (79.99 ≈ 80, 20.03 ≈ 20, 59.99 ≈ 60) and set m:w = 3:2, computing 80×3/5 and 80×2/5 to reach a boxed answer of 16. (6) A jar in ratio 8:x with equations 8y+5 = ny+30 and y(8−n) = 25, where the answer may be “Cannot be determined.” (7) A 72 L mixture in ratio 5:3, with unit = 72/8 = 9 L, milk = 45 L, water = 27 L; a related calculation shows 40×5/8 = 25 L. (8) A 180 L mixture in ratio 5:1, with w = 30 L and milk = 150 L; a crossed-out fraction (90+m)/18 appears. The session emphasizes ratio scaling, unit method, percentage-to-fraction conversion, and setting up linear equations for removed/added quantities.

Chapters

1. 0:00 – 2:00 00:00-02:00

   Title slide 'Mixture and Alligation' appears; instructor draws a green circle with plus signs and an arrow from 'MIXTURE', then begins writing the first example: 20 kg at Rs.40/kg and 30 kg at Rs.50/kg, with 'Rate' underlined.

2. 2:00 – 5:00 02:00-05:00

   Instructor writes the average-rate formula (20×40 + 30×50)/(20+30), computes (800+1500)/50 = 2300/50 = 46, and labels it CP per kg. The screen then transitions to an IBPS PYQ: 'Milk constitutes 60% by weight of an 80 g milk-and-water mixture. If 20 g is removed and 6 g water added, find the new ratio.'

3. 5:00 – 10:00 05:00-10:00

   The 80 g problem is solved: (60×80)/100 = 48 g milk, water = 80−48 = 32 g. Since 20/80 = 1/4 is removed, milk left = 48−12 = 36 g and water = 32−8+6 = 30 g, giving ratio 36:30 = 6:5. The next question (95 L, ratio 15:4) is introduced with red notes '95 Lit → 15/4' and scaling '15×5 = 75L', '4×5 = 20L'.

4. 10:00 – 15:00 10:00-15:00

   The 95 L problem continues: equation 75k/(20k+18) = 3/2 is set up. A shortcut appears: circled '0.6 → 40', line '95×40/100 = 38', and option E (38 L) is struck through. The next question begins: 'In a vessel, the quantity of water is 25% of the quantity of milk. Ten litres removed, 25 litres milk added.'

5. 15:00 – 20:00 15:00-20:00

   The 25%-water problem is solved using milk:water = 4n:n, total 5n. Removing 10 L gives 8 L milk and 2 L water removed; after adding 25 L milk, equations 'Milk = 4n−8+25 = 4n+17' and 'Fin w = n−2' are boxed, leading to 4n+17 = 5(n−2) and n = 27.

6. 20:00 – 25:00 20:00-25:00

   The n=27 result is confirmed with options 102–116 L visible. A new question appears: 'A container contains milk and water in ratio 3:2. After 75% removed, 40 L of a 40%-milk mixture is added; milk then constitutes 44 4/9% of the resultant.' This problem is introduced but not fully solved in sampled frames.

7. 25:00 – 30:00 25:00-30:00

   A problem with mixture A ratio 9:5 is shown, with red underlines on '20% more than the milk in A' and '25% more than the water in B'. Red notes approximate decimals: '79.99 = 80', '20.03 = 20', '59.99 = 60', and set ratio m:w → 3:2.

8. 30:00 – 35:00 30:00-35:00

   The 80 L problem is completed with '80×3/5' and '80×2/5', ending in a boxed answer of 16. A new question 'A jar contains milk and water in ratio 8:x' appears, with option 'Cannot be determined / निश्चित नहीं किया जा सकता' and red equations '8y+5 = ny+30', 'y(8−n) = 25'.

9. 35:00 – 40:00 35:00-40:00

   A 72 L mixture in ratio 5:3 is solved: '8 unit = 72', so unit = 9 L; milk = 45 L, water = 27 L. A related line shows '40×5/8 = 25 l'. The next problem (180 L, ratio 5:1) is introduced with notes 'w = 30' and milk = 150 L.

10. 40:00 – 40:48 40:00-40:48

    The 180 L problem continues with red calculations 'milk = 5/6×72 = 60', 'water = 1/6×72 = 12' (likely referring to a sub-quantity), and a crossed-out fraction '(90+m)/18'. The video ends with these working notes visible.

The lecture follows a consistent problem-solving pattern for mixture and alligation: (1) convert percentages or ratios into absolute quantities using the unit method; (2) track changes when mixture is removed (proportionally reducing both components) and when pure component is added; (3) set up a linear equation using the final ratio or percentage condition. Key techniques demonstrated include scaling ratios to match total volume (e.g., 15:4 with 95 L gives unit = 5 L), using fractions of removed quantity (e.g., removing 20 g from 80 g removes 1/4 of each component), and shortcut methods like computing the final water fraction to find removed quantity directly (95×40/100 = 38 L). The session covers at least eight distinct IBPS PYQs, emphasizing that ratio problems often reduce to simple linear equations once initial and final component quantities are expressed in terms of a variable (n, k, or y).