Answer:
28 cars
Step-by-step explanation:
Total number of cars and trucks = 20
Cars make up 40% of the collection
⇒ Number of cars = 40% of 20
= 0.4 x 20
= 8 cars
⇒ Number of trucks = total collection - number of cars
= 20 - 8
= 12 trucks
To calculate how many cars must be added to make the collection 75% cars, set up a ratio equation with x being the number of cars to be added:
(Added cars + existing cars) to total collection = 75%
⇒ x + 8 : x + 8 + 12 = 75 : 100
⇒ x + 8 : x + 20 = 75 : 100
[tex]\sf \implies \dfrac{x+8}{x+20}=\dfrac{75}{100}[/tex]
⇒ 100(x + 8) = 75(x + 20)
⇒ 100x + 800 = 75x + 1500
⇒ 100x -75x = 1500 - 800
⇒ 25x = 700
⇒ x = 28
Therefore he would need to add 28 cars to his collection to make his collection 75% cars.
Check
Number of cars = 8 + 28 = 36
Number of trucks = 12
Total collection = 36 + 12 = 48
Number of cars / total collection = 36/48 = 0.75 = 75%
