Question

#3) They say they have 50 total coins together made up of dimes and quarters. They also say that they have $7.25 total. How many quarters do they have?

A. 10
B.15.
C.20.
D.25​

Answer 1

B: 15 quarters

Explanation:

Step 1: Setup Coin Value and Coin Total Equation:

Coin Value Equation → 0.1d + 0.25q = $7.25 where d = dimes and q = quarters

Coin Total Equation → d + q = 50

Step 2: Rearrange Coin Total Equation in terms of dimes (d)

d = 50 - q ← Revised Coin Total Equation

Step 3: Plug in our Revised Coin Total Equation for d into our Coin Value Equation:

0.1(50 - q) + 0.25q = $7.25

0.1(50) - 0.1(q) + 0.25q = $7.25

5 - 0.1q + 0.25q = $7.25

5 + (0.25 - 0.1)q = $7.25

5 + 0.15q = $7.25

Step 4: Subtract 5 from each side of the equation to isolate q

5 - 5 + 0.15q = $7.25 - 5

0.15q = 2.25

Step 5: Divide each side of the equation by 0.15 to isolate q

0.15q

0.15

=

2.25

0.15

q = 15

Step 6: Using our value for q, Solve for d using our Coin Total Equation:

d + 15 = 50

Subtracting 15 from both sides, we get d + 15 - 15 = 50 - 15

d = 35

Summarizing our word problem, we see that 15 quarters and 35 dimes adds up to $7.25