
Shortcut Trick
Time for Rodney = 22 − 15 = 7 years and Time for Amit = 22 − 16 = 6 years.
Time difference = 1 year. Since Amit's money compounds for 1 year less, his principal must be larger by the 1-year interest multiplier.
Ratio of shares (Amit : Rodney) = (100 + 8) : 100 = 108 : 100 = 27 : 25.
Total ratio parts = 27 + 25 = 52 parts → ₹23400.
Amit's share (27 parts) = (23400 ÷ 52) × 27 = 450 × 27 = ₹12150.
∴ The correct answer is ₹12150.

Alternate Method
Total Wealth = ₹23400
Rodney (15 yrs)
Time = 7 years
Amit (16 yrs)
Time = 6 years
Rate = 8% CI p.a.
Equal Amount at 22 yrs
Given:
Total money distributed = ₹23400
Rate of interest (R) = 8% per annum compounded annually.
Time for Rodney = 22 − 15 = 7 years.
Time for Amit = 22 − 16 = 6 years.
Formula Used:
Amount in Compound Interest (A) = P × (1 + R/100)n
Calculation:
⇒ Let Amit's initial share be ₹A and Rodney's share be ₹(23400 − A).
⇒ Amount received by Amit after 6 years = A × (1 + 8/100)6
⇒ Amount received by Rodney after 7 years = (23400 − A) × (1 + 8/100)7
⇒ Since both receive the exact same amount when they turn 22, we equate the two values:
⇒ A × (1 + 8/100)6 = (23400 − A) × (1 + 8/100)7
⇒ A ÷ (23400 − A) = (1 + 8/100)1
⇒ A ÷ (23400 − A) = 108 / 100
⇒ A ÷ (23400 − A) = 27 / 25
⇒ 25 × A = 27 × (23400 − A)
⇒ 25A = 631800 − 27A
⇒ 25A + 27A = 631800
⇒ 52A = 631800
⇒ A = 631800 ÷ 52 = 12150
∴ The correct answer is ₹12150.

Additional Information
Ratio of Shares for Equal Amount (CI)
If a given sum is divided into two parts P1 and P2 such that their amounts are equal after t1 and t2 years respectively at R% compound interest, then P1 / P2 = (1 + R/100)t<sub>2</sub> − t<sub>1</sub>.
Effective Rate of Compound Interest
For 2 years, the effective compound interest rate is calculated using the successive percentage formula: R + R + (R × R)/100 = 2R + (R2/100) %.
Difference Between CI and SI
The difference between compound interest and simple interest for exactly 2 years on a principal P at a given rate R% per annum is given by PR2 / 10000.