2100 stickers are in 3 packets.
The 3rd packet has 300 stickers more than the total number of stickers in the 1st and 2nd packets.
The 2nd packet has 2 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 = 2 u

Number of stickers in the 1st packet and 2nd packet
= 1 u + 2 u
= 3 u

Number of stickers in the 3rd packet = 3 u + 300

Total number of stickers
= 1 u + 2 u + 3 u + 300
= 6 u + 300

6 u + 300 = 2100
6 u = 2100 - 300
6 u = 1800

1 u = 1800 ÷ 6 = 300

Number of stickers in the 3rd packet
= 3 u + 300
= 3 x 300 + 300
= 900 + 300
= 1200

Answer(s): 1200