Call the buses B and the cars C:
B + C = 7 [7 total vehicles]
45B + 5C = 195 [at 45 per bus and 5
per car, there were 195 students]
Use the first equation to express C in terms of B by subtracting B from both
sides:
B + C = 7 becomes C = 7 - B
Substitute 7 - B for C in the
second equation:
45B + 5(7 - B) = 195
Multiply out:
45B
+ 35 - 5B = 195
Simplify and subtract 35 from both sides:
40B =
160
Divide both sides by 40:
B = 4
There were 4 buses
and 3 cars used
