Pen - 1/5

Remain - 1-1/5=4/5
Book - 1/4x4/5 = 1/5
Had left - 1-1/5-1/5 = 3/5
3 thumb Drive - 3/4x3/5 = 9/20
1 thumb Drive = 3/20
Pen - 3/20/18=1/120
number of pens - 1/5 / 1/120 = 24

Pens: 24

The answer is as follows:


3/8-1/8+3/8/+1/8=6/8=3/4
4/12-1/3+1/12+1/12=2/12=1/6
3/9-1/3+?+1/9=1/3=3/9

?=2/9