Short Trick for Questions on Difference in Amount

Duration: 12 min

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This educational video is a lecture on simple and compound interest, presented by an instructor named Yash Jain. The video begins with an introductory slide that visually represents financial growth with a graph and coins, setting the context for the topic. The main content consists of two example problems. The first problem asks to find the rate of interest given that a sum of money amounts to Rs. 6200 in 4 years and Rs. 7100 in 7 years. The instructor solves this by first establishing the formula for the amount (A = P + SI) and then calculating the difference in the total amounts (A2 - A1) to find the interest earned over the 3-year period between the two time points. This leads to the calculation of the annual simple interest, which is then used to find the principal and finally the rate of interest. The second problem is similar, asking for the rate of interest when a sum amounts to Rs. 14880 after 3 years and Rs. 16800 after 5 years. The instructor applies the same method, calculating the interest for the 2-year period and then determining the annual interest and the rate. The video concludes with a 'Thank You' screen. The teaching style is direct, with the instructor writing out the formulas and calculations on a digital whiteboard, explaining each step clearly.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The video opens with a title slide for a lesson on 'Simple and Compound Interest'. The slide features a graphic of a rising graph and stacks of coins, symbolizing financial growth. The instructor, Yash Jain, appears in a small window on the right, introducing the topic. The text on the slide also indicates the lesson is from 'Knowledge Gate Educator' and covers the topic from 'Basic To Advance'. The instructor begins to explain the concept of simple interest, setting the stage for the problems to be solved.

  2. 2:00 – 5:00 02:00-05:00

    The first problem is presented on the screen: 'A sum of money amounted to Rs.6200 in 4 years and Rs.7100 in 7 years. Find the rate of interest.' The instructor begins the solution by writing the formula for the amount in simple interest: A = P + SI. He then writes the equations for the two scenarios: A1 = P + SI1 and A2 = P + SI2. He explains that the difference between the two amounts (A2 - A1) will give the interest earned over the 3-year period between the two time points, which is 7100 - 6200 = 900. This is a key step in the problem-solving process.

  3. 5:00 – 10:00 05:00-10:00

    The instructor continues solving the first problem. He uses the formula for simple interest, SI = (P * R * T) / 100, to express the interest for the 3-year period. He calculates that the interest for 3 years is 900, so the annual interest is 900 / 3 = 300. He then uses the amount after 4 years (6200) to find the principal: P = A - SI = 6200 - (300 * 4) = 6200 - 1200 = 5000. With the principal (P = 5000) and the annual interest (300), he calculates the rate of interest: R = (SI * 100) / (P * T) = (300 * 100) / (5000 * 1) = 6%. The final answer is R = 6%.

  4. 10:00 – 12:19 10:00-12:19

    The video transitions to a second problem: 'A sum of money amounted to Rs.14880 after 3 years and to Rs.16800 after 5 years. Find the rate of interest.' The instructor applies the same method. He calculates the interest for the 2-year period: 16800 - 14880 = 1920. The annual interest is 1920 / 2 = 960. He then finds the principal using the amount after 3 years: P = 14880 - (960 * 3) = 14880 - 2880 = 12000. Finally, he calculates the rate: R = (960 * 100) / (12000 * 1) = 8%. The video ends with a 'THANK YOU FOR WATCHING' screen.

The video provides a clear, step-by-step demonstration of how to solve simple interest problems where the principal is unknown. The core teaching method is to use the difference in the total amounts over a known time interval to find the annual interest. This annual interest is then used to back-calculate the principal and, finally, the rate of interest. The instructor consistently applies the formula A = P + SI and the formula for simple interest, SI = (P * R * T) / 100, to solve two distinct problems, reinforcing the method through repetition. The visual aid of writing on a digital whiteboard helps to follow the logical progression of the calculations.