1000 stickers are in 3 packets.
The 2nd packet has 100 stickers more than the total number of stickers in the 1st and 3rd packets.
The 3rd packet has 4 times as many stickers as the 1st packet.
How many stickers does the 2nd packet contain?
Choose the packet with the least stickers to be 1 u.

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

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

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

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

10 u + 100 = 1000
10 u = 1000 - 100
10 u = 900

1 u = 900 ÷ 10 = 90

Number of stickers in the 2nd packet
= 5 u + 100
= 5 x 90 + 100
= 450 + 100
= 550

Answer(s): 550