Marty has a piggy bank that contains 2.25. The piggy bank contains only quarters and dimes. There are twice as many dimes as quarters in the bank. How many dimes are in the piggy bank?

Answer 1

Start by setting out what we know in equations.

D = 0.10

Q = 0.25

X(0.10) + Y(0.25) = 2.25

X = 2Y

Now, replace the X in the longer equation with its known Y equivalent.

2Y(0.10) + Y(0.25) = 2.25

Multiply out the brackets

0.2Y + 0.25Y = 2.25

Add the Y values together

0.45Y = 2.25

Divide both sides by 0.45

Y = 5

So, now we can replace the Y in the longer equation

X(0.10) + 5(0.25) = 2.25

and resolve that

X(0.10) + 1.25 = 2.25

X(0.10) = 2.25 - 1.25

X(0.10) = 1.00

X = 10

So, there are ten dimes and five quarters.