Question

john has a collections of 20 minute cars and trucks. cars make up 40% of the collection. of john adds cars to the collections how many cars must he add to make up 75% of cars

Answer 1

Given that John has a collections of 20 cars and trucks and cars make up 40% of the collection.

Thus, the number of cars in the collection is given by


`(40)/(100) *20=8\, cars`

If john adds cars to the collections, the number of cars he must add to make up 75% of cars is obtained as follows:

Let x be the number of cars he must add, then


`(8+x)/(20+x) *100=75 \\ \\ \Rightarrow(8+x)/(20+x)=0.75 \\ \\ \Rightarrow8+x=0.75(20+x)=15 + 0.75x \\ \\ \Rightarrow x-0.75x=15-8 \\ \\ \Rightarrow0.25x=7 \\ \\ \Rightarrow x= (7)/(0.25) =28`

Therefore, the number of cars he must add to make up 75% of cars is 28 cars.