Question

Sophia's school took a field trip. a total of 21 vehicles were needed for the trip. some students took the bus, and some students car-pooled. there were 30 people on each bus and 4 people in each car. 318 people altogether attended the trip. how many buses were needed for the trip?

Answer 1

Let x be the number of buses, and y the number of cars.

`\left \{ {{x+y=21} \atop {30x+4y=318}} \right.`
We can solve for y in the first equation to get:

`y=21-x`
Now we can replace 21-x in our second equation, and solve for x:

`30x+4(21-x)=318`

`30x+84-4x=318`

`26x=234`

`x= (234)/(26)`

`x=9`

We can conclude that 9 buses were needed for the trip.