A person lent Rs. 12,000 to B for 3 years and Rs. 10,000 to C for 4 years on simple interest at the same rate of interest and received Rs 6,080 in all from both of them as interest. What is the annual rate of interest ?

8 percent 

Money lent by A to B 

Principal (P)=Rs 12000

Rate (R) = R %

Time (T)= 3 years

Interest I1=\(\frac{P×R×T}{100}\) =\(\frac{12000×R×3}{100}\)

Interest I1 = 360R

Money lent by A to C

Principal (P)=Rs 10,000

Rate (R) = R %

Time (T)= 4 years

Interest I2=\(\frac{P×R×T}{100}\) =\(\frac{10000×R×4}{100}\)

Interest I2  = 400R

ATQ

I₁+ I₂ = 6080

360R+400R=6080

760R=6080

R=\(\frac{6080}{760}\)

Rate = 8 % per annum