6th grade
posted by Susie .
Say you are at a bike shop. They sell tricycles, bicycles and unicycles. If there is a total of 150 wheels and 70 seats. If there are twice as many bicycles as tricycles how many of each type of bike do you have?

T + B + U = 70
B = 2T
U + 2B + 3T = 150

Solve those equations simultaneously.
2T + B = 80
2B = 80
B = 40
T = B/2 = 20
U = 70  40  20 = 10