Question

A large sports stadium has 21 000 seats. The seats are organized into blocks of either 400 or 450 seats. There are
3 times as many blocks of 450 seats as there are blocks of 400 400 seats. How many blocks are there.

Answer 1

Let the x-blocks have 400 seats

Then 3х-blocks for 450 seats

$400*x+450*3x=21000\\ 400x+1350x=21000\\ 1750x=21000\\ x=12$

12 blocks   have 400 seats

36 blocks    have 450 seats

48- all blocks

Answer: 48