Shortcut Trick
Ratio of shares (Older : Younger) = (1 + r/100)Δt : 1
Difference in time (Δt) = (24 − 13) − (24 − 14) = 11 − 10 = 1 year.
Ratio of Tushar : Ketan = (1 + 10/100)1 : 1 = 1.1 : 1 = 11 : 10.
Total units = 11 + 10 = 21 units → ₹23,100.
Tushar's share = (11 / 21) × 23,100 = ₹12,100.
∴ The correct answer is ₹12,100.
Alternate Method
Given:
Total wealth = ₹23,100
Age of Ketan = 13 years | Age of Tushar = 14 years
Time for Ketan (n1) = 24 − 13 = 11 years
Time for Tushar (n2) = 24 − 14 = 10 years
Rate of interest (r) = 10% per annum compounded annually.
Formula: Amount (A) = P(1 + r/100)n
Let the initial money given to Ketan be ₹K and to Tushar be ₹T.
⇒ K(1 + 10/100)11 = T(1 + 10/100)10
⇒ K(110/100)11 = T(110/100)10
⇒ K(1.1)11 = T(1.1)10
⇒ T / K = (1.1)11 / (1.1)10
⇒ T / K = 1.1 / 1 = 11 / 10
⇒ Ratio T : K = 11 : 10
⇒ Total sum = 11 + 10 = 21 units
⇒ 21 units = ₹23,100
⇒ 1 unit = 23,100 ÷ 21 = ₹1,100
⇒ Tushar's share = 11 × 1,100 = ₹12,100
∴ The correct answer is ₹12,100.
Additional Information
Compound Interest (CI)
It is the interest calculated on the initial principal, which also includes all of the accumulated interest from previous periods.
Amount in Compound Interest
A = P(1 + r/100)n, where A is the amount, P is the principal, r is the annual rate, and n is the time in years.
Ratio Distribution Rule
When the final amounts are equal, the person with the shorter duration (the older person) must receive a larger principal share.