Shortcut Trick
Ketan's investment time = 22 − 11 = 11 years, and Tushar's investment time = 22 − 12 = 10 years.
Since they receive equal amounts at age 22, the ratio of their principals is inverse to the ratio of their compounding multipliers.
Tushar's share : Ketan's share = (1 + 8/100)11−10 : 1 = 1.08 : 1 = 108 : 100 = 27 : 25.
Total ratio parts = 27 + 25 = 52 parts, which corresponds to the total wealth of ₹24700.
Tushar's share = (27 ÷ 52) × 24700 = 27 × 475 = ₹12825.
∴ The correct answer is ₹12825.
Alternate Method
Given:
Total initial money with Mandar = ₹24700
Ketan's age = 11 years, Tushar's age = 12 years
Target age for receiving the amount = 22 years
Rate of interest (R) = 8% compounded annually
Investment Timeline & Growth
Ketan (11 yrs)
₹ K
Tushar (12 yrs)
₹ T
Age 22
Amount Equal
Time = 11 Years @ 8%
Time = 10 Years @ 8%
Total Wealth = ₹24700 (K + T)
Formula Used:
Compound Interest Amount = P(1 + R/100)T
Calculations:
⇒ Time duration for Ketan's investment = 22 − 11 = 11 years.
⇒ Time duration for Tushar's investment = 22 − 12 = 10 years.
⇒ Let Ketan's initial share be K and Tushar's initial share be T.
⇒ According to the problem, amounts received by both at age 22 are equal.
⇒ K(1 + 8/100)11 = T(1 + 8/100)10
⇒ Dividing both sides by (1 + 8/100)10:
⇒ K(1 + 8/100)1 = T
⇒ T / K = (100 + 8) / 100 = 108 / 100 = 27 / 25
⇒ The ratio of Tushar's share to Ketan's share is 27 : 25.
⇒ Sum of ratio parts = 27 + 25 = 52 parts.
⇒ Total value of 52 parts = ₹24700
⇒ Value of 1 part = 24700 ÷ 52 = ₹475
⇒ Amount given to Tushar initially (T) = 27 parts = 27 × 475 = 12825.
∴ The correct answer is ₹12825.
Additional Information
Equal Amount Distribution in CI
If an amount is divided between two individuals such that their shares become equal after t1 and t2 years respectively at R% compound interest, the ratio of their initial shares is P1 : P2 = (1 + R/100)t2 − t1.
Compound Interest Formula
The amount A after time T with principal P and rate R% compounded annually is given by the equation A = P(1 + R/100)T.
Rule of Present Value
When final future values are equal, the person who has a shorter time period for the money to grow requires a larger initial principal (Present Value) to reach the identical target amount.