There are nickles and quarters worth $2.20 in total. If there are 28 coins, how many nickels are there?

There are 24 nickels

Step-by-step explanation:

Let x represent the number of nickels

Let y represent the number of quarters
—————————————————————

Value Value
Type Number of of
of of each all
Coin Coin Coin Coin
—————————————————————
Nickels | x | $0.05 | $0.05x
Quarters | y | $0.25 | $0.25y
—————————————————————
Totals 28 ——— $2.20
•••••••••••••••••••••••••••••••••••••••••••••••••

The first equation comes from the “Number of coins” column.

(Number of nickels) + (Number of quarters) = (total number of coins)

Equation: x + y = 28
—————————————————————
The second equation comes from the “value of all coins” column.

(Value of all nickels) + (Value of all quarters) = (Total value of all coins)

0.05x + 0.25y = 2.20

Remove the decimals by multiplying each term by 100:

5x + 25y = 220
—————————————————————
So we have the system of equations:

{x + y = 28
{5x + 25y = 202

Solve by substitution. Solve the first equation for y:

x + y = 28
y = 28 - x

Substitute (28 - x) for y in 5x + 25y = 220

5x + 25 (28 - x) = 220
5x + 700 - 25x = 220
-20x + 700 = 220
-20x = -480
x = 24

The number of nickels is 24.
————————————————————
Substitute in y = 28 - x
y = 28 - (24)
y = 4

The number of quarters is 4.
————————————————————
Checking:

24 nickels is $1.20 and 4 quarters is $1.00
That’s 28 coins.
Indeed $1.20 + $1.00 = $2.20
————————————————————