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

Number of stickers in the third packet = 1 u
Number of stickers in the first packet = 1 u + 30
Number of stickers in the second packet = 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 = 150
5 u = 150 - 120
5 u = 30

1 u = 30 ÷ 5 = 6

Number of less stickers in the first packet and third packet than the second packet
= (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 6 + 60
= 6 + 60
= 66

Answer(s): 66