DRDO Multi tasking staff Model paper 5

Tips & Tricks
Short trick∶
We know that,
Sum = Difference of CI and SI × (100/r)‌2
⇒ Sum = 40 × (100/8)‌2
⇒ Sum = Rs. 6250
Detailed solution∶
We know the formula for compound interest -
⇒ CI = [P { (1 +

r

100

)‌t − 1}]
Where,
CI = Compound interest
P = Principal
R = Rate of interest
T = Time period
Let the principal be P
CI = P (1 + 8/100)‌2-P = 104P/625
SI = P × 8 × 2/100 = 4P/25
CI - SI = 40
104P/625 - 4P/25 = 40
P = 40 × 625/4 = Rs. 6250