160 stickers are in 3 packets.
The third packet has 4 times as many stickers as the first packet.
The second packet is 20 less than the first packet.
How many less stickers are there in the first packet and the second packet than in the third 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 first packet = 1 u + 20
Number of stickers in the third packet = 4 x (1 u + 20) = 4 u + 80

Total number of stickers
= 4 u + 80 + 1 u + 20 + 1 u
= 4 u + 1 u + 1 u + 80 + 20
= 6 u + 100

6 u + 100 = 160
6 u = 160 - 100
6 u = 60

1 u = 60 ÷ 6 = 10

Number of less stickers in the first packet and second packet than the third packet
= (4 u + 80) - (1 u + 20 + 1 u)
= (4 u + 80) - (2 u + 20)
= 4 u - 2 u  + 80 - 20
= 2 u + 60
= 2 x 10 + 60
= 20 + 60
= 80

Answer(s): 80