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I’m in 7th grade and forgot how to add and subtract whole numbers and fractions, can someone explain it to me? Example: 13 2/3 - 4 1/3 = __

User Drahkar
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1 Answer

13 votes
13 votes

(This is how I explain it)

If they have the same denominator, don't change it

but if they have different denominators, change it

So you first subtract the fractions:

2/3 - 1/3: it equals 1/3 because of the numerators: 2-1=1 (but also put the denominator)

Then just multiply the whole numbers: 13 - 4 = 9

Ok now just put them together: 9 1/3

But if the subtraction looks like this:

8 1/3 - 3 2/3

then for the 1/3 just add another whole to it. (since you cannot subtract 1/3 - 2/3 and get a number over 0)

Like:

Since the denominator is 3, then add 3 to the 1/3 numerator: 1 + 3 = 4

So there's 4/3. even though this is an improper fraction, you can still subtract it.

Look:

4/3 - 2/3 = 2/3

But since the 8 got 1 whole took away, it becomes 7.

So then you subtract 7 - 3 which is 4

So the answer for this one is 4 2/3

Adding is easier

Now if you add 4 1/5 + 6 2/5, you just add the fractions and whole number.

1/5 + 2/5 = 3/5

Now add the whole numbers: 4 + 6 = 10.

Put it together: 10 3/5 is the answer

If you add like 15 1/4 + 5 3/4 then just add the fractions and whole number:

1/4 + 3/4 = 4/4: but since it's 4/4, then we convert it into a whole number: 1.

So it's basically 15 + 5 = 20, then add that whole number: 1

Answer: 21

Now for this one:

5 4/9 + 1 2/3

Since they have different denominators, you have to get the same denominator for each one. If you get a different denominator, it means you have to change the numerator too.

Like this:

2/3, you can multiply the numerator and demoniator by 3 to get the denominator 9. (which matches 4/9!)

2 x 3 = 6

3 x 3 = 9

Since we have 6 and 9, our new fraction is 6/9

We don't have to do anything to the other fraction since it already has 9 as a denominator.

Now add:

6/9 + 4/9 = 10/9

Inproper fractions:

10/9, subtract 9 from the numerator: (since 9 is the denominator)

10- 9 = 1

turn the extra into a fraction and the 9/9 into 1.

since we have 1 leftover, the fractions combined are 1 1/9

We can basically just add

5 + 1 + 1 1/9 = 7 1/9

here is the last short one:

6/10 + 2/3

Since 3 cannot be multiplied by a whole number to 10, we have to change both.

We can multiply both denominators together:

6/10:

6 x 3 = 18

10 x 3 = 30

2/3:

2 x 10 = 20

3 x 10 = 30

So our new equation is:

18/30 + 20/30 = 38/30

But, since it's an improper fraction, we should convert it into a mixed number:

38-30=8

Ok since we could subtract it, we have: 1

But we have 8 extra

so the answer is 1 8/30

We can simplify it though.

2 is the highest number we can go for both numerator and denominator

8 divided by 2: 4

30 divided by 3: 15

So the correct answer is: 1 4/15

i hope this helped, sorry i'm not that good at explaining

User GuiSim
by
3.0k points
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