Solve 5x − 15 = 30

The solution of 5x − 15 = 30 is x = 9.

5x - 15 = 30\ \Rightarrow\ x = 9

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The lines y = 5x − 15 and y = 30 meet at x = 9. 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.
$5x - 15 = 30$
2
Add 15 to both sides:
$5x - 15 + 15 = 30 + 15 \ \Rightarrow\ 5x = 45$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{45}{5} \ \Rightarrow\ x = 9$
4
Check: put x = 9 back into the equation.
$5\cdot9 - 15 = 45 - 15 = 30 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 15 = 30\ \Rightarrow\ x = 9 \]
\[ 5x - 15 = 30 \]
\[ 5x - 15 + 15 = 30 + 15 \ \Rightarrow\ 5x = 45 \]
\[ \frac{5x}{5} = \frac{45}{5} \ \Rightarrow\ x = 9 \]
\[ 5\cdot9 - 15 = 45 - 15 = 30 \checkmark \]

Trying values of x in 5x − 15 = 30

x	5x − 15	Equals 30?
7	20	no
8	25	no
9	30	yes
10	35	no
11	40	no

Questions

What is x in 5x − 15 = 30?

The solution of 5x − 15 = 30 is x = 9.

How do you solve 5x − 15 = 30?

Add 15 to both sides to get 5x = 45, then divide both sides by 5 to get x = 9.

How do I check the answer?

Replace x by 9: 5(9) − 15 = 30, which is 30.

Solve 5x − 15 = 30

How to work it out

Trying values of x in 5x − 15 = 30

Questions

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