James has a collection of 20 miniature cars and trucks. Cars make up 40% of the collection. If James adds only cars to his collection, how many cars must he add to make the collection 75% cars?

Guest Jul 9, 2019

#1**+1 **

Let the new cars to be added =C

0.75[C + 20] =0.40[20] + C

0.75C + 15 = 8 + C

0.75C - C = 8 - 15

- 0.25C = - 7

C = 7 / 0.25

C = 28 - New cars that must be added to his collection.

Guest Jul 9, 2019

#2**+2 **

**James has a collection of 20 miniature cars and trucks. Cars make up 40% of the collection. If James adds only cars to his collection, how many cars must he add to make the collection 75% cars?**

\(\begin{array}{|rcll|} \hline \mathbf{\text{cars }} &=& \mathbf{20\cdot40\ \%} \\\\ &=& \dfrac{20\cdot 40}{100} \\ &=& \mathbf{8} \\ \hline \end{array} \)

\(\begin{array}{|rcll|} \hline \mathbf{(20+x)\cdot75\ \%} &=& \mathbf{8+x} \\\\ (20+x)\cdot 0.75 &=& 8+x \\ 15+ 0.75x &=& 8+x \\ 7+ 0.75x &=& x \\ x- 0.75x &=& 7 \\ 0.25x &=& 7 \\ x &=& \dfrac{7}{0.25} \\ \mathbf{ x } &=& \mathbf{28} \\ \hline \end{array}\)

He must add **28** cars to make the collection **75%** cars.

heureka Jul 9, 2019

#3**+1 **

40% of the cars and trucks are cars = .40 * 20 = 8

Let x be the number of cas he needs to add to have 75% cars....so we have

[ 8 + x ]

_______ = .75 multiply both sides by 20 + x

20 + x

8 + x = .75 [ 20 + x ]

8 + x = 15 + .75x subtract .75x, 8 from both sides

.25x = 7 divide both sides by .25

x = 28

So....he needs to add 28 cars to have 75% cars

CPhill Jul 9, 2019