170 stickers are in 3 bags.
The third bag has 3 times as many stickers as the first bag.
The second bag is 30 less than the first bag.
How many less stickers are there in the first bag and the second bag than in the third bag?
Choose the bag with the least stickers to be 1 u.

Number of stickers in the second bag = 1 u
Number of stickers in the first bag = 1 u + 30
Number of stickers in the third bag = 3 x (1 u + 30) = 3 u + 90

Total number of stickers
= 3 u + 90 + 1 u + 30 + 1 u
= 3 u + 1 u + 1 u + 90 + 30
= 5 u + 120

5 u + 120 = 170
5 u = 170 - 120
5 u = 50

1 u = 50 ÷ 5 = 10

Number of less stickers in the first bag and second bag than the third bag
= (3 u + 90) - (1 u + 30 + 1 u)
= (3 u + 90) - (2 u + 30)
= 3 u - 2 u  + 90 - 30
= 1 u + 60
= 1 x 10 + 60
= 10 + 60
= 70

Answer(s): 70