Answer:
15 nickels and 28 quarters.
Explanation:
Let the number of nickels = n
Let the number of quarters = q
Sarah has 43 coins:
[tex]\begin{gathered} n+q=43 \\ \implies n=43-q \end{gathered}[/tex]
1 nickel = 5 cents = $0.05
1 quarter = 25 cents =$0.25
She runs her change through the bank coin machine and gets back $7.75
[tex]0.05n+0.25q=7.75[/tex]
We then solve the two equations simultaneously:
[tex]\begin{gathered} 0.05n+0.25q=7.75 \\ 0.05(43-q)+0.25q=7.75 \\ 2.15-0.05q+0.25q=7.75 \\ 0.2q=7.75-2.15 \\ 0.2q=5.6 \\ q=28 \end{gathered}[/tex]
Finally, solve for the number of nickels:
[tex]\begin{gathered} n=43-q \\ =43-28 \\ n=15 \end{gathered}[/tex]
Sarah started with 15 nickels and 28 quarters.