120 stickers are in 3 packets.
The first packet has 3 times as many stickers as the third packet.
The second packet is 20 less than the third packet.
How many less stickers are there in the third packet and the second packet than in the first packet?
Choose the packet with the least stickers to be 1 u.

Number of stickers in the second packet = 1 u
Number of stickers in the third packet = 1 u + 20
Number of stickers in the first packet = 3 x (1 u + 20) = 3 u + 60

Total number of stickers
= 3 u + 60 + 1 u + 20 + 1 u
= 3 u + 1 u + 1 u + 60 + 20
= 5 u + 80

5 u + 80 = 120
5 u = 120 - 80
5 u = 40

1 u = 40 ÷ 5 = 8

Number of less stickers in the third packet and second packet than the first packet
= (3 u + 60) - (1 u + 20 + 1 u)
= (3 u + 60) - (2 u + 20)
= 3 u - 2 u  + 60 - 20
= 1 u + 40
= 1 x 8 + 40
= 8 + 40
= 48

Answer(s): 48