A borrows Rs. 8000 at $12 \%$ per annum simple interest and B borrows Rs. 9100 at $10 \%$ per annum simple interest. In how many years will their amounts be equal?
- A18 years
- B20 years
- ✓22 years
- D24 years
$R _1=12 \%$
$R _2=10 \%$
$P _1=$ Rs. 8000
$P _2=$ Rs. 9100
Let their amounts be equal in $T$ years.
$\text { Amount }_1=\text { S.I. }_1+P_1$
$=\frac{P_1 \times r_1 \times T}{100}+P_1$
$=960 T+8000$
$\text { Amount }_2=\text { S.I. }_2+P_2$
$=\frac{P_2 \times r_2 \times T}{100}+P_2$
$=\frac{9100 \times 10 \times T}{100}+9100$
$=910 T+9100$
$\text { Amount } t_1=\text { Amount }$
$\Rightarrow 960 T+8000=910 T+9100$
$\Rightarrow 960 T-910 T=9100-8000$
$\Rightarrow 50 T=1100$
$\Rightarrow T=22$
Hence, after 22 years their amounts will be equal.