Fractions for Parents Part 3
Fractions for parents part 3 by www.guruparents.com
This short video gives a refresher on subtracting fractions, so you the parent can help with your child’s homework without feeling inadequate!
1. Simple subtraction
3/7 – 2/7
When the fractions have the same base or denominator you just subtract the numerators. So in this case it’s just 3 minus 2, giving the answer 1/7.
2. Finding a common denominator
In this example, the denominator is not the same so I need to find a common one.
The lowest common denominator is 10 as 10 is divisible by both 5 and 10.
So to convert 3/5 into tenths, since I multiplied 5 by 2 to get 10 I need to do the same to the numerator. 3 x 2 = 6. 6/10.
And now I can subtract the numerators. 7 minus 6 is 1; the answer is 1/10.
3. Subtracting Mixed Numerals
Subtracting mixed numerals is often very straightforward, as is the case here.
All I need to do first is find a common denominator for the fractions. And the lowest common denominator is 6, so 4 2/3 becomes 4 4/6.
Now I just subtract the whole numbers – 4 minus 2 is 2 – and then the fractions – 4/6 minus 1/6 is 3/6. The answer is 2 3/6 which simplifies to 2 ½.
4. Subtracting harderd mixed numerals
Sometimes subtracting mixed numerals can be a bit tougher, specifically when the first fraction is smaller than the second. Here are a couple of methods to handle this.
4 1/3 - 2 3/5
First, as always get a common denominator. 15 will be the common denominator. I needed to multiply 3 by 5 to get 15, so I do the same to the numerator. 5 times 1 is 5. And over here I needed to multiply 5 by 3 to get 15, so I multiply the numerator by 3 too to get 9.
Now I have the same base so I can subtract the numerators but 5 minus 9 is going to be less than zero - which is a problem.
So, I'm going to borrow. I'll take 1 from the whole number. So 4 becomes 3. And now I add my 1 to the fraction. Another way of writing 1 is 15/15. So 15 + 5 = 20: I now have 20/9. Incidentally a little trick here is that you can just add the numerator and the denominator together to get this: 15 + 5 = 20.
So, now I can subtract. 20 minus 9 is 11. 3 minus 2 is 1. The answer is 1 and 11/15.
Another way to approach this question is to change both fractions to improper fractions. It's a less elegant method but it works and may be easier for some kids to do.
So what's 4 1/3 as an improper fraction? 4 times 3 is 12 plus 1 is 13, so 13/3.
And 2 3/5 - 2 times 5 is 10 plus 3 is 13/5.
So, we need a common denominator. Again, it'll be 15.
I multiplied 3 by 5 to get 15. So I do the same for the numerator: 13 times 5 is 65. 65/15.
And to get 5 to 15 i multiplied by 3. I do the same to the numerator: 3 times 13 is 39: 39/15.
65 minus 39 is 26. So 26/15. Finally, to convert this back to a mixed numeral. 15 goes into 26 just the once with 11 left over so we have 1 11/15 - the same as above.
So this method is just as effective, although it often involves a few harder sums.
And that's it - simple. And that's just about as hard as non algebraic fractions ever get. I hope you enjoyed the video!
Watch video Fractions for Parents Part 3 online without registration, duration hours minute second in high quality. This video was added by user GuruParents 21 May 2015, don't forget to share it with your friends and acquaintances, it has been viewed on our site 15,39 once and liked it 2 people.