Question

the different between the simple and compound interest on a certain sum of money for 4 years at 6% p.a is rs 168.75. what is the sum? ​

Answer 1

Explanation:

Let the principle is P and rate of interest is 15%.

Time =2 years

Then, for CI:

CI =P(1+

100

R

)

2

−P

CI =P[(1+

100

15

)

2

−1] ......[∵(a+b)

2

=a

2

+b

2

+2ab]

⇒ CI =P[1+

100

2×15

+

10000

(15)

2

−1]

⇒ CI =P[1+

100

30

+

10000

225

−1]

⇒ CI =P[

10

3

+

400

9

]

⇒ CI =P[

400

120+9

]

CI =

400

129P

For SI:

⇒ SI =

100

PRT

⇒ SI =

100

P×15×2

⇒ SI =

100

30P

According to the question, we have

CI−S.I=Rs.144

⇒

400

129P

−

100

30P

=144

⇒

400

129P−120P

=144

⇒P=

9

144×400

P= Rs. 6400