Use the substitution method to solve:
f + t = 15
5f + 20t = 180
Check Format
Equation 1 is in the correct format.
Check Format
Equation 2 is in the correct format.
Rearrange Equation 2 to solve for f:
5f + 20t = 180
Subtract 20t from both sides to isolate f:
5f + 20t - 20t = 180 - 20t
5f = 180 - 20t
Now divide by 5:
| 5f | |
| 5 |
| = |
| 180 - 20t |
| 5 |
Revised Equation 2:
| f = | 180 - 20t |
| 5 |
Plug Revised Equation 2 value into f:
1(f) + t = 15
1 * ((180 - 20t)/5) + t = 15
((180 - 20t)/5) + t = 15
Multiply equation 1 through by 5
5 * (((180 - 20t)/5) + t = 15)
5 * (((180 - 20t)/5) + t = 15)
180 - 20t + 5t = 75
Group like terms:
-20t + 5t = 75 - 180
-15t = -105
Divide each side by -15
| -15t | |
| -15 |
| = |
| -105 |
| -15 |
| t = | -105 |
| -15 |
t = 7
Plug this answer into Equation 1
1f + 1(7) = 15
1f + 7 = 15
1f = 15 - 7
1f = 8
Divide each side by 1
| 1f | |
| 1 |
| = |
| 8 |
| 1 |
| f = | 8 |
| 1 |
f = 8
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