If the simple interest on a certain sum is due for some years at 6 % is ?180, and the discount at 5 % on the same amount is ?140. Find the sum and the time.

Here, r₁ = 20% and r₂ = 5%
? Required percentage
= r₁ + r₂ - (r₁ x r₂)/100%
= 20 + 5 - (20 x 5)/100
= 25 - 1
=24%

? Marked price of an article = ? 500
The selling price of article after discount 20% and 10%
= 500 x {(100 - 20) / 100} x {(100 - 10) / 100}
= 500 x (80/100) x (90/100)
= ? 360

Let labelled price of TV = ? R
? SP of the TV = [R x (100 - 20)] / 100 = ? 4R/5
But 16800 - 800 = 4R/5
? x = (16000 x 5)/4 = ? 20000

Here, r = 20% and r₁ = 15%
Required profit per cent =[ r(100 - r₁)/100] - r₁
= [20(100 - 15)/100] - 15
= 17 - 15
= 2%