A sells an article to B at gain of 25% B sells it to C at a gain of 20% and C sells it to D at a gain 10%. If D pays Rs. 330 for it, how much did it cost to A?

Answer: Option A

First Method
Let Cost Price for A was 100
Then CP for B = 100 + 25% of 100 = 125
CP for C = 125 + 20% of 125 = 150
CP for D = 150 + 10% of 150 = 165
But, D pay Rs. 330, Then it must be equal to
165 = 330
1 = $$\frac{330}{165}$$
100 = $$\frac{330\times 100}{165}=200$$
Thus, CP for A = Rs. 200

Short-cut
A's CP = $$330\times \frac{100}{125}\times \frac{100}{120}\times \frac{100}{110}$$     = Rs. 200