Solve 10x − 1 = 99

The solution of 10x − 1 = 99 is x = 10.

10x - 1 = 99\ \Rightarrow\ x = 10

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The lines y = 10x − 1 and y = 99 meet at x = 10. 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.
$10x - 1 = 99$
2
Add 1 to both sides:
$10x - 1 + 1 = 99 + 1 \ \Rightarrow\ 10x = 100$
3
Divide both sides by 10:
$\frac{10x}{10} = \frac{100}{10} \ \Rightarrow\ x = 10$
4
Check: put x = 10 back into the equation.
$10\cdot10 - 1 = 100 - 1 = 99 \checkmark$

LaTeX source of the formulas on this page

\[ 10x - 1 = 99\ \Rightarrow\ x = 10 \]
\[ 10x - 1 = 99 \]
\[ 10x - 1 + 1 = 99 + 1 \ \Rightarrow\ 10x = 100 \]
\[ \frac{10x}{10} = \frac{100}{10} \ \Rightarrow\ x = 10 \]
\[ 10\cdot10 - 1 = 100 - 1 = 99 \checkmark \]

Trying values of x in 10x − 1 = 99

x	10x − 1	Equals 99?
8	79	no
9	89	no
10	99	yes
11	109	no
12	119	no

Questions

What is x in 10x − 1 = 99?

The solution of 10x − 1 = 99 is x = 10.

How do you solve 10x − 1 = 99?

Add 1 to both sides to get 10x = 100, then divide both sides by 10 to get x = 10.

How do I check the answer?

Replace x by 10: 10(10) − 1 = 99, which is 99.

Solve 10x − 1 = 99

How to work it out

Trying values of x in 10x − 1 = 99

Questions

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