# Large Marbles cost 25 cent and small marbles cost 10 cents. Sally buys 18 marbles for a total cost of 2.85. How many large marbles does she buy?

Apr 22, 2018

7

#### Explanation:

Let $S$ be the number of small marbles
Let $L$ be the number of large marbles.

The large marbles cost $0.25 each, therefore, the amount that she spent on large marbles is: $0.25L

Add to that the cost of the small marble that she bought:

$0.25L+$0.10S

We are told that equals $2.85 $0.25L+ $0.10S =$2.85" [1]"

We are told that $L + S = 18$ which can be written as:

$S = 18 - L \text{ [2]}$

Substitute equation [2] into equation [1]:

$0.25L+$0.10(18-L) = $2.85 Use the distributive property: $0.25L+ $1.80-$0.10L = $2.85 Combine like terms: $0.15L = $1.05 Divide both sides by $0.15

L = ($1.05)/($0.15)

$L = 7$