Video: Finding the Missing Fraction When Adding Two Fractions with the Same Denominator

Complete the following: 2/9 + _ = 2/3.

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Video Transcript

Complete the following: two-ninths plus blank equals two-thirds.

Almost immediately, we notice that we have different denominators in parts of this problem. Before we can solve it, we’ll need to make sure that we’re dealing with all common denominators. We can keep two over nine. And then we’ll take this two-thirds and create a fraction over the denominator of nine. I know that three times three equals nine. And if I multiply the denominator by something, I also need to multiply the numerator by that same amount. Two times three equals six.

Now, we have the equation two-ninths plus blank equals six-ninths. When we’re adding fractions, we’re working with fractions that have a common denominator. That means we need a nine as our denominator here. Now we know, two over nine plus something over nine has to equal six over nine. When we add fractions with common denominators, we only add their numerators. We need to know two plus what equals six. Two plus four equals six.

And that shows us that two-ninths plus four-ninths equals six-ninths. The missing value is four over nine.

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