90 stickers are in 3 bags.
The 1st bag has 5 times as many stickers as the 2nd bag.
The 3rd bag is 3 times as many stickers as the 2nd bag.
How many less stickers are there in the 2nd bag than in the 1st bag and 3rd bag?
Choose the bag with the least stickers to be 1 u.

Number of stickers in the 2nd bag = 1 u
Number of stickers in the 1st bag = 5 x 1 u = 5 u
Number of stickers in the 3rd bag = 3 x 1 u = 3 u

Total number of stickers
= 1 u + 5 u + 3 u
= 9 u

9 u = 90
1 u = 90 ÷ 9 = 10

Number of stickers less in the 2nd bag than in the 1st and 3rd bags
= Total number of stickers in 1st and 3rd bag - Number of stickers in 2nd bag
= 5 u + 3 u - 1 u
= 7 u 
= 7 x 10
= 70

Answer(s): 70