Sol : Option D Explanation: Rate of interest = 20%. So P (1 + 20/100)^{t} > 2P
→(6/5)^{t} > 2 = (1.2)^{t} > 2
→Putting the values of t = 1, 2, 3, 4, only t = 4 years is satisfied.
→t = 4 years.

Q.2. A sum of money at compound interest amounts to four times of itself in 2 years. In how many years will it be 16 times of itself?

a) 18 Year

b) 27 Year

c) 9 Year

d) 6 Year

e) 4 Year

Sol : Option E Explanation: Rs. 1 becomes Rs. 4 in 2 years. i.e. 1 → 4 (2 years)
So, 4 → 16 in another 2 years
Hence, we can say that Rs. 1 becomes Rs. 16 in 2 + 2 = 4 years.
Hence, the answer is option E

Q.3. A sum of money at compound interest amounts to eight times of itself in 3 years. In how many years will it be 512 times of itself?

a) 28 Year

b) 24 Year

c) 9 Year

d) 16 Year

e) 14 Year

Sol : Option C Explanation: Rs. 1 becomes Rs. 8 in 3 years. i.e. 1 → 8 in 3 years.
So, 8 → 64 in another 3 years.
Also, 64 → 512 in another 3 years.
Hence, we can say that Rs. 1 becomes Rs. 512 in 3 + 3 + 3 = 9 years.
Hence, the answer is option C

Q.4.In what time will a man receive Rs. 51 as compound interest on Rs. 625 at 4% p.a. compounded annually?

a) 4 1/2 Year

b) 2 1/2 Year

c) 2 Year

d) 3 Year

e) 5 Year

Sol : Option C Explanation: CI = Rs.51 therefore, A = 625 +51 = 676.
→ 676 = 625(1 + 4/100)^{t}
→ t = 2 years.

Q.5.In what time will a man receive Rs. 1449 as compound interest on Rs. 10000 at 7% p.a. compounded annually?

a) 4 Year

b) 2 1/2 Year

c) 2 Year

d) 5 Year

e) 3 Year

Sol : Option C Explanation: CI = Rs.1449 therefore, A =10000 + 1449 = Rs. 11449
→ 11449 = 10000(1 + 7/100)^{t}
→ t = 2 years.

Q9.A certain sum of money invested @ 40 % p.a. compounded half-yearly amounts to Rs. 5760 in 1 year. What is the sum (in Rs.)?

A. B. C. D. E.

a) 2100

b) 4000

c) 1900

d) 2000

e) 2200

Sol : Option B Explanation: Half yearly, therefore, R= 40 /2 % = 20% and T = 1 × 2 = 2 years
Applying formula, 5760=P (1 + 20/100)^{2}
P= 5760 X 25/36 = Rs. 4000

Q10.A sum of money is invested at compound interest compounded annually. The interests in two successive years were Rs. 150 and Rs. 168. Then the rate percent was