Erin has 72 stamps in her stamp drawer along with a quarter, two dimes and seven pennies. She has 3

Erin has 72 stamps in her stamp drawer along with a quarter, two dimes and seven pennies. She has 3 times as many 3-cent stamps as 37-cent stamps and half the number of 5-cent stamps as 37-cent stamps. The value of the stamps and coins is $8.28. How many 37-cent stamps does Erin have?

Number of stamps:

• Number of 37 cent stamps = s
• Number of 3-cent stamps = 3s
• Number of 5-cent stamps = 0.5s

Value of stamps and coins:

• 37 cent stamps = 0.37s
• 3-cent stamps = 3 * 0.03 = 0.09s
• 5-cent stamps = 0.5 * 0.05s = 0.025s
• Quarter, 2 dime, 7 pennies = 0.52

Add them up:
0.37s + 0.09s + 0.025s + 0.52 = 8.28

Solve for s in the equation 0.37s + 0.09s + 0.025s + 0.52 = 8.28

Step 1: Group the s terms on the left hand side:
(0.37 + 0.09 + 0.025)s = 0.485s

Step 2: Form modified equation
0.485s + 0.52 = + 8.28

Step 3: Group constants:
We need to group our constants 0.52 and 8.28. To do that, we subtract 0.52 from both sides
0.485s + 0.52 - 0.52 = 8.28 - 0.52

Step 4: Cancel 0.52 on the left side:
0.485s = 7.76

Step 5: Divide each side of the equation by 0.485
0.485s/0.485 = 7.76/0.485
s = 16

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