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An amount of Rs 10000 is deposited in bank A for a certain number of years at a simple interest of 5% per annum. On maturity, the total amount received is deposited in bank B for another 5 years at a simple interest of 6% per annum. If the interests received from bank A and bank B are in the ratio 10 : 13, then the investment period, in years, in bank A is

Solution

✅ Correct Option: 2

Let's recall that Simple Interest = Principal × Rate × Time ÷ 100


Principal (P) = Rs 10000

Rate (R) = 5% per annum

Time = T years (this is what we need to find!)

Using Simple Interest formula: SI=P×R×T100SI = \tfrac{P \times R \times T}{100}

Interest from Bank A = 10000×5×T100=500T\tfrac{10000 \times 5 \times T}{100} = 500T


Maturity amount from Bank A = Original Principal + Interest Earned

= 10000+500T10000 + 500T

Important: This entire maturity amount becomes the new principal for Bank B.


Now this entire amount goes to Bank B:

New Principal = 10000+500T10000 + 500T

Rate = 6% per annum

Time = 5 years

Interest from Bank B = (10000+500T)×6×5100\tfrac{(10000 + 500T) \times 6 \times 5}{100}

=(10000+500T)×30100= \tfrac{(10000 + 500T) \times 30}{100}

=30(10000+500T)100= \tfrac{30(10000 + 500T)}{100}

=3000+150T= 3000 + 150T


We're told that interests from Bank A and Bank B are in ratio 10:13.

Interest from Bank AInterest from Bank B=1013\tfrac{\text{Interest from Bank A}}{\text{Interest from Bank B}} = \tfrac{10}{13}

500T3000+150T=1013\tfrac{500T}{3000 + 150T} = \tfrac{10}{13}


500T×13=(3000+150T)×10500T \times 13 = (3000 + 150T) \times 10

6500T=30000+1500T6500T = 30000 + 1500T

6500T−1500T=300006500T - 1500T = 30000

5000T=300005000T = 30000

T=6T = 6 years

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