Question 145·Easy·Math

After you undo the $+8$, you will get a simpler equation involving $2x$ on one side. What should you do next to get $x$ by itself?

Once you know the value of $x$ for the original equation, solve each answer choice for $x$. Which choice gives the same $x$-value as the original equation?

Instead of solving each choice completely, think about what operation you could do to both sides of $2x + 8 = 20$ to get an equation of the form $2x = \text{(number)}$, like the ones in the answer choices.

In one expression line, type 2x+8=20. Desmos will display the solution for $x$ (for example, as a solution statement or a point on the $x$-axis). Note this $x$-value.

On new lines, type each choice exactly as an equation: 2x=28, 2x=12, 2x=10, and 2x=8. For each line, look at the $x$-value that Desmos shows as the solution.

Compare the $x$-value from the original equation with the $x$-values from each choice. The correct answer is the choice whose equation has the same $x$-value as the original equation.

Start with the given equation:

Undo the $+8$ by subtracting $8$ from both sides:

Now divide both sides by $2$ to solve for $x$:

So the original equation has the solution $x = 6$.

Now solve each answer choice for $x$:

• Choice A: $2x = 28$
  Divide by $2$: $x = 14$.
• Choice B: $2x = 12$
  Divide by $2$: $x = 6$.
• Choice C: $2x = 10$
  Divide by $2$: $x = 5$.
• Choice D: $2x = 8$
  Divide by $2$: $x = 4$.

Only choice B gives $x = 6$, which matches the solution of the original equation. Therefore, the equation that has the same solution as $2x + 8 = 20$ is $2x = 12$ (choice B).