Question

Bernie counted the cars and motorcycles that passed his house in 45 minutes. He counted 20 vehicles and 72 tires. How many cars passed his house?
8
12
16
20

Answer 1

let x = cars and y = motorcycles..

now the equation for the number of cars is

x + y = 20

the number of tires is

4x + 2y = 72 ( a car has 4 tires, a motorcycle has 2 tires)

so you have to solve the equations simulataneously.

the easiest way is to use substitution and look to eliminate y

so from the 1st equation

x + y= 20

rewrite it with y as the subject

y = 20 - x

now substitute it into the 2nd equation

4x + 2y = 72

or

4x +2(20 - x) = 72

now you can sole for x, the number of cars

Answer 2

so then it would be 4 motorcycles and 16 cars?

Answer 3

correct