Trying to explain my daughter's homework to her?

There are two basic rules for handling decimals:

1. Addition/Subtraction: line up the decimals and put in zeros if need be, then add like a normal addition problem. For example, if you have 13.4 + 4.75 you'd write it like:

13.40

04.75

_____ +

18.15

See how the decimals line up and you added in the 0 to 13.4?

2. Multiplication... count the number of digits you have behind the decimal point and then toss out the decimal point. When you've got an answer, add the decimal point back into the number, counting the same number of digits from the right.

For example, if you have 2.5 X 1.55, that'd be 3 digits behind the decimal (one for the .5 and two for the .55). Remember that and then multiple the numbers as if they didn't have decimals: 25 X 155 = 3875. Now, reinsert the decimal 3 places from the right: 3.875.

3. Division: this is too hard to show without paper, so tell your daughter to bring home her book when she gets to that chapter.

Adding decimals should be easier than fractions.

And don't worry my students used to 'forget' their workbooks often. I finally had to call their parents and insist they check for them. I'm glad you do.

The key to adding decimals is to place one on top of the other and add down, but when you do, the decimal points have to line up.

3.9

+ 12.5 wrong

3.9

+ 12.5 right

So for example if you have 8.9 + 3.05 you would write it

8.9

+ 3.05

Now the right side must line up as well, so we add a 0 as a place marker to the short line.

8.90

+ 3.05

Add straight down and we get

11.95

Simple no? And of course if the numbers added up to more than 10 you'd carry the 1 as you would with regular addition.

Multiplying decimals:

Tip: However many digits are on the right side of a decimal point when you start, that's how many should be on the right of the answer.

So, if I'm multiplying 2.6 and 8.9, there are two numbers on the right side of a decimal (6 and 9) so my answer is going to have two numbers on the right.

The easy way to mulitply is to forget about the decimals entirely. So if we just multiply 26 and 89 as normal we'd get 2314

Now move the decimal two places to the left (since we said our answer would have two numbers to the right of the decimal) and we get 23.14 Done.

Dividing decimals.

This one's a bit harder. Easiest way is to get rid of the decimals entirely

For example:

14.4

____

1.2

If we multiply this fraction by 10/10 we get

144/12

That's much easier to solve yes? The answer is then 12.

How about 2.5/0.05

One number has only 1 number on the right of the decimal, the ohter has two numbers on the right of the decimal (0 and 5) so we multiply it by 100/100

Our new fraction is then 250/5 which becomes 50.

So to review:

Adding: Line up the decimals

Multiplying: take out the decimals, then put them back in the answer (just count how many places to move it!)

Fractions: Multiply by some multiple of 10 on top and bottom to eliminate all decimals.

I don't quite understand the term simplify decimal. I seen it used for fractions and there are references to "simplify decmal" in Google. There is no example. 3.4 + 8.09 = 11.49. How do you simplify that?

This isn't a direct answer to your question, but if you will check out www.rosemond.com, you will find some wonderful and liberating information for dealing with children, teachers, and homework. (No, the numbers of children who leave their math books at school are legion...nothing unusual there!)

its really easy you just put 3.4 under 8.09 and then add it.

then divd. the number in to the answer. then divd. it by how many numbers they are.

The first one, just add. 3.40+8.09=11.49