1800 stickers are in 3 bags.
The 2nd bag has 100 stickers more than the total number of stickers in the 1st and 3rd bags.
The 3rd bag has 4 times as many stickers as the 1st bag.
How many stickers does the 2nd bag contain?
Choose the bag with the least stickers to be 1 u.

Number of stickers in the 1st bag = 1 u
Number of stickers in the 3rd bag = 4 u

Number of stickers in the 1st bag and 3rd bag
= 1 u + 4 u
= 5 u

Number of stickers in the 2nd bag = 5 u + 100

Total number of stickers
= 1 u + 4 u + 5 u + 100
= 10 u + 100

10 u + 100 = 1800
10 u = 1800 - 100
10 u = 1700

1 u = 1700 ÷ 10 = 170

Number of stickers in the 2nd bag
= 5 u + 100
= 5 x 170 + 100
= 850 + 100
= 950

Answer(s): 950