1100 stickers are in 3 packets.
The 3rd packet has 900 stickers more than the total number of stickers in the 1st and 2nd packets.
The 2nd packet has 4 times as many stickers as the 1st packet.
How many stickers does the 3rd 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 2nd packet = 4 u

Number of stickers in the 1st packet and 2nd packet
= 1 u + 4 u
= 5 u

Number of stickers in the 3rd packet = 5 u + 900

Total number of stickers
= 1 u + 4 u + 5 u + 900
= 10 u + 900

10 u + 900 = 1100
10 u = 1100 - 900
10 u = 200

1 u = 200 ÷ 10 = 20

Number of stickers in the 3rd packet
= 5 u + 900
= 5 x 20 + 900
= 100 + 900
= 1000

Answer(s): 1000