Question

If in 1 year ratio of principal and amount is 20:21 then find the rate of interest

Answer 1

Given :

• Principal : Amount = 20:21
• Time = 1 year

To find : Rate of interest

Let : Common factor of Principal and amount = x

Formula used :

• Amount (A) = Principal(P) + Intrest(I)
• I = P× r × t

Solution :

Principal : Amount = 20x : 21x

Let, Principal = 20x

this gives Amount = 21x

Interest = Amount - Principal

I = 21x - 20x

I = x

I = P×r× t

$\sf \implies \: x = 20x \times \dfrac{r}{100} \times 1 \\ \\ \sf \implies \: r \: = \: \dfrac{x \times 100}{20x} \\ \\ \sf \implies \: r \: = 5 \%$

ANSWER = Rate of interest = 5% p.a.