Solve 10x − 9 = 31

The solution of 10x − 9 = 31 is x = 4.

10x - 9 = 31\ \Rightarrow\ x = 4

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The lines y = 10x − 9 and y = 31 meet at x = 4. 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.
$10x - 9 = 31$
2
Add 9 to both sides:
$10x - 9 + 9 = 31 + 9 \ \Rightarrow\ 10x = 40$
3
Divide both sides by 10:
$\frac{10x}{10} = \frac{40}{10} \ \Rightarrow\ x = 4$
4
Check: put x = 4 back into the equation.
$10\cdot4 - 9 = 40 - 9 = 31 \checkmark$

LaTeX source of the formulas on this page

\[ 10x - 9 = 31\ \Rightarrow\ x = 4 \]
\[ 10x - 9 = 31 \]
\[ 10x - 9 + 9 = 31 + 9 \ \Rightarrow\ 10x = 40 \]
\[ \frac{10x}{10} = \frac{40}{10} \ \Rightarrow\ x = 4 \]
\[ 10\cdot4 - 9 = 40 - 9 = 31 \checkmark \]

Trying values of x in 10x − 9 = 31

x	10x − 9	Equals 31?
2	11	no
3	21	no
4	31	yes
5	41	no
6	51	no

Questions

What is x in 10x − 9 = 31?

The solution of 10x − 9 = 31 is x = 4.

How do you solve 10x − 9 = 31?

Add 9 to both sides to get 10x = 40, then divide both sides by 10 to get x = 4.

How do I check the answer?

Replace x by 4: 10(4) − 9 = 31, which is 31.

Solve 10x − 9 = 31

How to work it out

Trying values of x in 10x − 9 = 31

Questions

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