Solve 5x − 15 = 20

The solution of 5x − 15 = 20 is x = 7.

5x - 15 = 20\ \Rightarrow\ x = 7

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The lines y = 5x − 15 and y = 20 meet at x = 7. The solution of the equation is the x-coordinate of the point where the two sides are equal.

How to work it out

1
The goal is to get x alone. Undo the operations in the opposite order: first the subtraction, then the multiplication.
$5x - 15 = 20$
2
Add 15 to both sides:
$5x - 15 + 15 = 20 + 15 \ \Rightarrow\ 5x = 35$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{35}{5} \ \Rightarrow\ x = 7$
4
Check: put x = 7 back into the equation.
$5\cdot7 - 15 = 35 - 15 = 20 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 15 = 20\ \Rightarrow\ x = 7 \]
\[ 5x - 15 = 20 \]
\[ 5x - 15 + 15 = 20 + 15 \ \Rightarrow\ 5x = 35 \]
\[ \frac{5x}{5} = \frac{35}{5} \ \Rightarrow\ x = 7 \]
\[ 5\cdot7 - 15 = 35 - 15 = 20 \checkmark \]

Trying values of x in 5x − 15 = 20

x	5x − 15	Equals 20?
5	10	no
6	15	no
7	20	yes
8	25	no
9	30	no

Questions

What is x in 5x − 15 = 20?

The solution of 5x − 15 = 20 is x = 7.

How do you solve 5x − 15 = 20?

Add 15 to both sides to get 5x = 35, then divide both sides by 5 to get x = 7.

How do I check the answer?

Replace x by 7: 5(7) − 15 = 20, which is 20.

Solve 5x − 15 = 20

How to work it out

Trying values of x in 5x − 15 = 20

Questions

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