Question

This is a 1st-grade math problem 12 + _____ = 13 + 7

Answer 1

Explanation:

12 + 1 = 13 + 7=20

Answer 2

I'll say that the unknown number is "x", then our expression is

`12+x=13+7`

And we want to find out the value of "x"

To solve it, we will first do the sum on the right side:

`12+x=20`

Now, we want to have "x" alone on the left side, then, let's subtract 12 on both sides

`\begin{gathered} 12-12+x=20-12 \\ \\ x=20-12 \\ \\ x=8 \end{gathered}`

Then the value of x is 8, let's test it:

`\begin{gathered} 12+8=13+7 \\ \\ 20=20 \end{gathered}`

Correct! 12 + 8 is 20. Then, the unknown number is 8