model 3 combination of si & ci Practice Questions Answers Test with Solutions & More Shortcuts

Question : 21 [SSC CPO S.I.2003]

If the compound interest on a certain sum for 2 years at 3% per annum is Rs.101.50, then the simple interest on the same sum at the same rate and for the same time will be

a) Rs.98.25

b) Rs.90.00

c) Rs.100.00

d) Rs.95.50

Answer: (c)

Let the sum be P.

101.50 = P$[(1 + 3/100)^2 - 1]$

[Since, C.I. = P$[(1 + r/100)^n - 1]$]

101.50 = P$[(103/100)^2 - 1]$

=P$({10609 - 10000}/10000)$

P = Rs.${101.50 × 10000}/609 = Rs.1015000/609$

S.I. = ${1015000 × 2 × 3}/{609 × 100}$ = Rs.100

Using Rule 10,
The simple interest for a certain sum for 2 years at an annual rate interest R% is S.I., then
C.I. = S.I.$(1 + R/200)$

Here, C.I. = Rs.101.50, R = 3%, S.I. = ?

C.I. = S.I.$(1 + R/200)$

101.50 = S.I.$(1 + 3/200)$

S.I. = ${101.50 × 200}/203$ = Rs.100

Question : 22 [SSC CGL Tier-I 2013]

There is 100% increase to an amount in 8 years, at simple interest. Find the compound interest of Rs.8000 after 2 years at the same rate of interest.

a) Rs.2125

b) Rs.2500

c) Rs.2250

d) Rs.2000

Answer: (a)

Using Rule 1,

Let S.I. = Rs.100, & Principal = Rs.100

Rate = $\text"S.I. × 100"/\text"Principal × Time"$

= ${100 × 100}/{100 × 8} = 25/2$%

C.I. = P$[(1 + r/100)^T - 1]$

= 8000$[(1 + 25/200)^2 - 1]$

= 8000 $(81/64 - 1)$

= ${8000 × 17}/64$ = Rs.2125

Question : 23 [SSC CGL Tier-I 2016]

The simple interest on a certain sum of money for 2 years at 5% is Rs.1600. The compound interest at the same rate after 3 years interest compound annually, is

a) Rs.2535

b) Rs.2520

c) Rs.2555

d) Rs.2522

Answer: (d)

Principal = $\text"S.I. × 100"/\text"Time × Rate"$

= ${1600 × 100}/{5 × 2}$ = Rs.16000

C.I. = P$[(1 + R/100)^T - 1]$

= 16000$[(1 + 5/100)^3 –1]$

= 16000$[(21/20)^3 - 1]$

= $16000(9261/8000 - 1)$

= ${16000 × 1261}/8000$ = Rs.2522

Question : 24 [SSC CAPFs 2016]

The simple interest on a sum of money for 3 years is Rs. 240 and the compound interest on the same sum, at the same rate for 2 years is Rs. 170. The rate of interest is :

a) 5$5/17$%

b) 8%

c) 12$1/2$

d) 29$1/6$%

Answer: (c)

Since, S.I. for 3 years = Rs.240

S.I. for 2 years = $240/3$× 2 = Rs.160

${PR × 2}/100$ = 160

PR = 160 × 50 = 8000...(i)

Again, C.I. - S.I. = 170 - 160 = Rs.10

${PR^2}/10000$ = 10

${8000 × R}/10000$ = 10

R = $100/8 = 25/2 = 12{1}/2$%

Question : 25 [SSC CGL Tier-I 2016]

If the simple interest on a sum of money for 2 years at 5% per annum is Rs.50, the compound interest on the same at the same rate and for the same time is :

a) Rs.50.05

b) Rs.50.50

c) Rs.51.50

d) Rs.51.25

Answer: (d)

Principal = $\text"S.I. × 100"/ \text"Time × Rate"$

= ${50 × 100}/{2 × 5}$ = Rs.500

C.I. = P$[(1 + R/100)^T - 1]$

= 500$[(1 + 5/100)^2 - 1]$

= 500$[(1 + 1/20)^2 - 1]$

= 500$[(21/20)^2 - 1]$

= 500$(441/400 - 1)$

= ${500 × 41}/400$ = Rs.51.25

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