Question

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?

Answer 1

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`