Question 505·Easy·Math

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$\dfrac{y}{5} + 9 = 21$

What value of $y$ is the solution to the given equation?

Your answer

In a linear equation, the unknown appears only to the first power. If the unknown is divided and then a number is added, undo those operations in reverse order: subtract first, then multiply. A Desmos regression can also find the unknown from the original equation. Don't mistake the value of the fraction for the value of the unknown.

Hints

Hint 1
An inverse operation undoes an operation. The $9$ is added to the whole fraction, so subtract $9$ from both sides first. What does that leave equal to $y/5$ ?
Hint 2
The expression $y/5$ means $y$ divided by $5$ . Finding the value of $y/5$ doesn't yet tell you $y$ . What operation would undo that division?

Step-by-step

Undo the addition, then solve in Desmos
Step 1
Find the value of the fraction
The $9$ is added after $y$ is divided by $5$ , so undo the addition first. Subtract $9$ from both sides:
$\begin{aligned}\frac{y}{5}+9-9&=21-9\frac{y}{5}&=12.\end{aligned}$
Step 2
Read the value of $y$ in Desmos
The $12$ is the fraction's value, not $y$ . To solve the original equation in Desmos, type $\frac{y_1}{5}+9\sim21$ . The subscript makes $y_1$ the number to find, and $\sim$ tells Desmos to match the two sides. Under PARAMETERS, Desmos shows $y_1=60$ . So the solution is $y=60$ . Grid in 60.

Question 505·Easy·Math

Strategy

Hints

Step-by-step

Lessons that teach this

Study Hints

Strategy

Hints

Step-by-step

Lessons that teach this