DRDO Multi tasking staff Model paper 10

We know that simple interest (S.I.)
S.I. = (P.r.t)/100, Where P = principal, r = rate and t = time.
So, total debt discharged = (amount discharged in 1st year) + (amount discharged in 2nd year) + (amount discharged in 3rd year) + (amount discharged in 4th year) + (amount discharged in 5th year)
i.e
Total debt discharged = P + (P + Pr/100) + (P + 2Pr/100) + (P + 3Pr/100) + (P + 4Pr/100)
Putting, total debt discharged = 6000 and r = 10% we get
6000 = 6P
⇒ P = Rs. 1000