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?

1 Answer
Apr 22, 2018

Answer:

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" [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#