Question

A sum of money invested at compound interest amounts to Rs 800 in 3 yrs and to Rs 840 in 4 yrs. Find the rate of interest per annum with steps shown

Answer 1

$c.i = p(100 + r) \div 100 \times t$

p=800
t=3 year
p=840
t=4 year
=800 (100+x)÷100×3
=800(100x×100x×100x)÷100÷100÷100
=800 (x+x+x)
=800 (3x)
=800÷3=x
=166.67=x
840 (100+x)÷100×4
840 (100x+100x+100x+100x)÷100÷100÷100÷100
840 (4x)
840÷4=x
210=x
please tell me it is right
if it is right