Question

17. In what time will the interest on Rs 2500 be Rs. 500 at the rate of 10% per year?

18. At what rate of interest will a sum of money double in 20 years?

[Hint: in 20 years Rs. 100 will become 2×100 = Rs 200. So interest is 200-100]​

Answer 1

Answer:

17. 2 Years.

18. 5%

Step-by-step explanation:

17. Given:

Simple Interest = Rs. 500

Principal = Rs. 2500

Rate = 10% p.a.

Asked:

Time = ?

Solution:

We know that,

Simple Interest = $\frac{PRT}{100}$

500 =  2500 × $\frac{10}{100}$ × Time

Time = $\frac{500 × 100}{2500 × 10}$

Time = 2 years

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18. Given:

Time = 20 years

Let Principal be 'x',

then Amount = 2x

Simple Interest = Amount - Principal

⇒ 2x - x

⇒ x

Simple Interest = x

Now we know that,

Simple Interest = $\frac{PRT}{100}$

x = $\frac{x × R × 20}{100}$

R% = $\frac{x × 100}{x × 20}$

Rate% = 5%

= At the rate of 5%  a sum of money double in 20 years.

Answer 2

Answer:

(17) 2 years

(18) 5%

hope it goes well