Solve 5x − 15 = 40

The solution of 5x − 15 = 40 is x = 11.

5x - 15 = 40\ \Rightarrow\ x = 11

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The lines y = 5x − 15 and y = 40 meet at x = 11. 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.
$5x - 15 = 40$
2
Add 15 to both sides:
$5x - 15 + 15 = 40 + 15 \ \Rightarrow\ 5x = 55$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{55}{5} \ \Rightarrow\ x = 11$
4
Check: put x = 11 back into the equation.
$5\cdot11 - 15 = 55 - 15 = 40 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 15 = 40\ \Rightarrow\ x = 11 \]
\[ 5x - 15 = 40 \]
\[ 5x - 15 + 15 = 40 + 15 \ \Rightarrow\ 5x = 55 \]
\[ \frac{5x}{5} = \frac{55}{5} \ \Rightarrow\ x = 11 \]
\[ 5\cdot11 - 15 = 55 - 15 = 40 \checkmark \]

Trying values of x in 5x − 15 = 40

x	5x − 15	Equals 40?
9	30	no
10	35	no
11	40	yes
12	45	no
13	50	no

Questions

What is x in 5x − 15 = 40?

The solution of 5x − 15 = 40 is x = 11.

How do you solve 5x − 15 = 40?

Add 15 to both sides to get 5x = 55, then divide both sides by 5 to get x = 11.

How do I check the answer?

Replace x by 11: 5(11) − 15 = 40, which is 40.

Solve 5x − 15 = 40

How to work it out

Trying values of x in 5x − 15 = 40

Questions

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