Solve 5x − 9 = 91

The solution of 5x − 9 = 91 is x = 20.

5x - 9 = 91\ \Rightarrow\ x = 20

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The lines y = 5x − 9 and y = 91 meet at x = 20. 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.
$5x - 9 = 91$
2
Add 9 to both sides:
$5x - 9 + 9 = 91 + 9 \ \Rightarrow\ 5x = 100$
3
Divide both sides by 5:
$\frac{5x}{5} = \frac{100}{5} \ \Rightarrow\ x = 20$
4
Check: put x = 20 back into the equation.
$5\cdot20 - 9 = 100 - 9 = 91 \checkmark$

LaTeX source of the formulas on this page

\[ 5x - 9 = 91\ \Rightarrow\ x = 20 \]
\[ 5x - 9 = 91 \]
\[ 5x - 9 + 9 = 91 + 9 \ \Rightarrow\ 5x = 100 \]
\[ \frac{5x}{5} = \frac{100}{5} \ \Rightarrow\ x = 20 \]
\[ 5\cdot20 - 9 = 100 - 9 = 91 \checkmark \]

Trying values of x in 5x − 9 = 91

x	5x − 9	Equals 91?
18	81	no
19	86	no
20	91	yes
21	96	no
22	101	no

Questions

What is x in 5x − 9 = 91?

The solution of 5x − 9 = 91 is x = 20.

How do you solve 5x − 9 = 91?

Add 9 to both sides to get 5x = 100, then divide both sides by 5 to get x = 20.

How do I check the answer?

Replace x by 20: 5(20) − 9 = 91, which is 91.

Solve 5x − 9 = 91

How to work it out

Trying values of x in 5x − 9 = 91

Questions

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