A. 7 years

B. 10 years

**C. 15 years**

D. 20 years

Explanation:

Let principal be Rs x and the rate is R % p.a.

Then X × (1 + R/100)^{5} = 2x

=> (1 + R/100)^{5} = 2

Let x × (1 + R/100)^{t} = 8x

=> (1 + R/100)^{t} = 8 = 2^{3}

={(1 + R/100)^{5} }^{3}

=> (1 + R/100)^{t} = (1 + R/100)^{15}

=> T = **15 Years**

### Related Mcqs:

- A sum of money placed at C.I. interest doubles itself in 5 years. It will amount to eight times itself at the same rate of interest in?
A. 7 years

B. 10 years

**C. 15 years**

D. 20 years - A sum of money place at compound interest doubles itself in 4 years. In how many years will it amount to eight times itself?
A. 16

B. 8

**C. 12**

D. 20 - The sum of money at compound interest amounts to thrice itself in 3 years. In how many years will it be 9 times itself?
A. 18

B. 12

C. 9

**D. 6** - Simple interest on a certain sum of money for 3 years at 8% per annum is half the compound interest on Rs. 4000 for 2 years at 10% per annum. The sum placed on simple interest is:_______?
A. Rs. 1550

B. Rs. 1650

**C. Rs. 1750**

D. Rs. 2000 - A man invests a certain sum of money at 6% per annum simple interest and another sum at 7% per annum simple interest. His income from interest after 2 years was Rs. 354. One-forth of the first sum is equal to one-fifth of the second sum. The total sum invested was :
A. Rs.3100

**B. Rs.2700**

C. Rs.2200

D. Rs.1800 - A sum of Rs.4800 is invested at a compound interest for three years, the rate of interest being 10% p.a., 20% p.a. and 25% p.a. for the 1st, 2nd and the 3rd years respectively. Find the interest received at the end of the three years.
A. Rs.2520

**B. Rs.3120**

C. Rs.3320

D. Rs.2760

E. None of these - If the simple interest on a sum of money for 2 years at 5% per annum is Rs. 50, what is the compound interest on the same sum at the rate and for the same time?
**A. Rs. 51.25**

B. Rs. 52

C. Rs. 54.25

D. Rs. 60 - The compound interest on a certain sum of money for 2 years at 10 % per annum is Rs.420. The simple interest on the same sum at the same rate and for the same time will be_______?
A. Rs.350

B. Rs.375

C. Rs. 380

**D. Rs. 400** - A sum amount to Rs.1344 in two years at simple interest. What will be the compound interest on the same sum at the same rate of interest for the same period?
A. Rs.150

B. Rs.140

C. Rs.130

**D. Data insufficient for the answer** - The simple interest on Rs.12000 at a certain rate of interest in five years is Rs.7200. Find the compound interest on the same amount for five years at the same rate of interest.
A. Rs.3502.80

B. Rs.3052.40

C. Rs.3054.8

**D. Rs.3052.80**

E. None of these