1800 stickers are in 3 packets.
The 1st packet has 800 stickers more than the total number of stickers in the 2nd and 3rd packets.
The 3rd packet has 3 times as many stickers as the 2nd packet.
How many stickers does the 1st packet contain?
Choose the packet with the least stickers to be 1 u.

Number of stickers in the 2nd packet = 1 u
Number of stickers in the 3rd packet = 3 u

Number of stickers in the 2nd packet and 3rd packet
= 1 u + 3 u
= 4 u

Number of stickers in the 1st packet = 4 u + 800

Total number of stickers
= 1 u + 3 u + 4 u + 800
= 8 u + 800

8 u + 800 = 1800
8 u = 1800 - 800
8 u = 1000

1 u = 1000 ÷ 8 = 125

Number of stickers in the 1st packet
= 4 u + 800
= 4 x 125 + 800
= 500 + 800
= 1300

Answer(s): 1300