In 50 gm alloy of gold and silver the gold is 80 % by weight. How much gold should be mixed with this alloy so that the weight of gold would become 95 %?

A. 15
B. 36
C. 48
D. 60
Explanation:
Case I if lady sits on the reserved seat, then 2 men can occupy seats from 4 vacant seats in = 4P2 = 4×3 = 12ways
Case II if lady does not sit on reversed seat, then I. Woman can occupy a seat from four seats in 4 ways. I. man can occupy a seat from 3 seats in 3 ways, also I. man left can occupy a seat from remaining two seats in 2 ways.
Therefore, Total ways = 4x3x2 = 24ways
From case I and case II
Total number of ways = 12+24 = 36