Susie emptied and old piggy bank that she forgot she had and found $6.30 in nickels and dimes if there is a total of 90 coins, how many nickels does she have?

You can either do this with 2 variables or one.

In one variable you have the equation... Let x represent the nickels, so there are 90-x dimes
.05x + (90-x)(.10) = 6.30
Solve for x

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To find the number of nickels Susie has, we need to solve a system of equations. Let's use variables to represent the number of nickels and dimes she has.

Let's say the number of nickels is 'n' and the number of dimes is 'd'.

We are given two pieces of information. First, we know the total value of the coins is $6.30. Since there are 90 coins in total, we can set up the equation:

0.05n + 0.10d = 6.30 (the value of each nickel is $0.05, and the value of each dime is $0.10)

The second piece of information is that there are a total of 90 coins, so:

n + d = 90

Now we have a system of two equations:

0.05n + 0.10d = 6.30 (Equation 1)
n + d = 90 (Equation 2)

To solve this system, we can use substitution or elimination method.

Let's solve it using the elimination method.

We want to get rid of the decimals in Equation 1, so let's multiply both sides of Equation 1 by 100 to eliminate the decimals:

100 * (0.05n + 0.10d) = 100 * 6.30

This simplifies to:

5n + 10d = 630

Now we have:

5n + 10d = 630 (Equation 3)
n + d = 90 (Equation 2)

Next, we'll multiply Equation 2 by 5 to eliminate the variable 'n':

5 * (n + d) = 5 * 90

This simplifies to:

5n + 5d = 450 (Equation 4)

Now we have:

5n + 10d = 630 (Equation 3)
5n + 5d = 450 (Equation 4)

By subtracting Equation 4 from Equation 3, we can eliminate 'n':

(5n + 10d) - (5n + 5d) = 630 - 450
5d = 180

By dividing both sides of the equation by 5, we get:

d = 36

Now we know that the number of dimes is 36.

To find the number of nickels, we substitute this value of 'd' back into Equation 2:

n + 36 = 90

By subtracting 36 from both sides of the equation, we get:

n = 54

So, Susie has 54 nickels.