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### Course: Arithmetic>Unit 13

Lesson 5: Adding and subtracting mixed numbers with unlike denominators

# Subtracting mixed numbers with regrouping (unlike denominators)

To subtract mixed numbers, first align the whole numbers and fractions so they can be subtracted separately. If the fractions have different denominators, find a common denominator and convert them accordingly. If the fraction on the bottom is larger, regroup by borrowing from the whole number on top. This will allow you to complete the subtraction.

## Want to join the conversation?

• how did he suddenly change from only having 4/9 to adding 4/9 + 9/9? Where did the 9/9 fraction come from? It's a bit confusing.
• Sal took a whole (9/9) from 17 because if 4/9 minus 6/9 it will be negative. And 17 becomes 16.
16 13/9 is the same thing as 17 4/9. Since if you change 13/9 into a mixed number (1 4/9), then add it to 16, it's 17 4/9.
Hope this helps
• how did you turn the 2/3 into 6/9?
• You can always multiply by 1 and get the same (equivalent) thing. He multiplied by 3/3 which is like a nickname for 1. Multiplying the tops (2*3=6) and the bottoms(3*3=9). The bottoms(denominators) is why we chose the 3/3 version of 1 in the first place. That was the way to get common denominator.
• you cant add/subtract if your denomeraters are not the same.like 5/9 and 2/6.they have denomerator of 54 so now it would be 30/54 and 18/54 which would be 48/54.hope it helps!
• I don't get it.
• I am assuming you are confused with the regrouping part- since the subtrahend's numerator is bigger than the minuend, you can make the minuend's numerator bigger by regrouping. You take from the whole number and add it into the fraction. So, in the video, from the mixed fraction 17 4/9, 17 becomes 16, and you add what you took away, one whole = 9/9, into the fraction itself which becomes 4/9 + 9/9 = 13/9, then proceed with the subtraction.
• Me literally studying with my mom and she getting angry at me
• What if you need to be simplified? I still don't get simplifying fractions with whole numbers.
• At the end of the problem, if your answer can be simplified, do it!
For example, if you have 5 6/12 , you can automatically see that the "6/12" can be simplified down to 1/2. You don't need to do anything to the 5 because you never simplify the whole number. Your final answer would be 5 1/2
Did this help?
• is there something that can help me understand better?
• I would recommend re-watching the video and doing the practice multiple times to get better.