Of 75 cars that were inspected 12 needed brake repair and 18

Of 75 cars that were inspected, 12 needed brake repair and 18 needed exhaust system repair. If the brakes or exhaust systems on 50 of the cars did not need repair, how many cars needed both brake and exhaust system repairs?

Solution

Let x be cars which needed brake repair and exhaust syetm repair

So, only brake repair = 12 - x

only exhaust repair = 18 -x

Both = x

So, total of above = 12-x +18-x + x= 30 -x = 75 - 50

30 -x = 25

x = 5

So, 5 cars needed repair of both