Answer
Mary has:
15 nickels
10 dimes
5 quarters
Work Step by Step
A nickel is 5 cents ($\$0.05$), a dime is 10 cents ($\$0.10$), and a quarter is 25 cents ($\$0.25$)
Let
$x$=number of quarters
Then
$2x$=number of dimes
$2x+5$=number of nickels
The total value of the coins is $\$3.00$. Thus,
$0.25(x) + 0.10(2x) + 0.05(2x+5) = 3.00
\\0.25x +0.20x + 0.10x+0.25= 3.00
\\0.55x+0.25=3.00
\\0.55x=3.00-0.25
\\0.55x=2.75
\\x=5$
Therefore, there are:
5 quarters
$2(5) = 10$ dimes
$10+5=15$ nickels
