Why do we have to line up decimals when we add and subtract, but not when we multiply and divide? ?

Question

Why do we have to line up decimals when we add and subtract, but not when we multiply and divide? ? Omg plz help!

Answer 1

Very happy to help.



In addition and subtraction of any numbers, you have to line up the place values, i.e., the ones line up, then the 10s column, then the 100s colums and so on. Like this:



1 0 0

+ 1 0

--------

1 1 0

--------



Adding and subtracting decimals are the same. You need to line up the tenths, hundredths, thousandths,... columns.



Multiplying decimals, as you're probably aware of is just straight-forward multiplication. The final answer has the total number of decimal places of the two numbers you were multiplying.

0.2 (one decimal) X 0.12 (2 decimal places) = 0.024 (3 decimal places).



Division of decimals, you still do have to line up the decimal point. Especially doing it this way:



5 . 2 8

________

2 ) 1 0 . 5 6



Hope that helps!



Umm the formatting is wrong, just a quick edit. I can't fix it up, so the above division might not line up properly!

Answer 2

It's ok, it's not a stupid question. Just follow the directions that I listed below, and you will understand. ADDING DECIMALS When adding decimals, the decimals ALWAYS must be lined up. Ex. When adding 2.3 and 3.6, you would write the problem with the 2 over the 3 and the 3 over the 6, so the answer would be 5.9 SUBTRACTING DECIMALS When subtracting decimals, set the problem up the same way that you do when you add decimals, except the only difference is that you subtract. Ex.) 2.3 - 2.1 What you would do for this problem, is line the decimals up, and then subtract the 2 - 2 and the 3-1, so when you are done the problem, it should be .2 MULTIPLYING DECIMALS When multiplying decimals, you don't need to line up the decimals, but instead the decimal gets moved to the left at the end of the equation. Ex.)1.2*1.4 The first thing you do is write it like this: 1.2 x1.4 just remember that the computer will not line up the problem I wrote above, so just know that the 1 is over the 1 and the 2 is over the 4 and the decimals are lined up. so you multiply the 4*2 and the 4*1 and then put a zero to hold the place value, and then put in the answer 1*2 and the 1*1 and write it like this: 1.2 x 1.4 or 1.2 x1.4 ____ 48 140 then add the 48 and the 140 and get 182 DO NOT FORGET!!!!!!!!!!! you now must move the decimal point 2 times to the left, because the problem includes 2 decimal. when you move the decimal over you will get the final answer of 1.82 DIVIDING DECIMALS When dividing decimals, you must always remember to: move the decimal as many times to the right as you need when the divisor is a decimal. (the computer will not line up the dividing sign correctly, so just know how to write out the problem) For example: ___ .2 | 4 You have to move the decimal one time to the right BUT DON'T FORGET!!!! whatever you do to that number, you have to do to the dividend. so the problem should now say: ___ 2 | 40 and the answer will be 20 I hope that this explanation helps you to better understand how to do these types of problems. GOOD LUCK!!!!!!!!!!

Answer 3

Lining Up Decimals

Answer 4

http://www.math.com/school/subject1/lessons/S1U1L5GL.html



I don't know if this link will help, but my thought is that adding and subtracting you are staying with the same number of decimal places and with * & / you put the decimal in after you do the equation

Answer 5

for subtrac/addition its to make sure that u dont add/subtract the wrong digit and for multiplaction and division it doesnt matter bcuz u have to do either digit anyway.