By selling 12 oranges for one rupee, a man loses 20%. How many for a rupee should he sell to get gain of 20%?

Suppose he buys 12 oranges. Then S.P. = Re. 1
Now, 80 : 1 : : 120 : R
∴ R = (1 x 120) / 80 = 3/2
∴ For Rs. 3/2, oranges sold = 12
For Re. 1 oranges sold = (12 x 2) / 3 = 8
So, he must sell them at 8 for a rupee.