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half of 99 and a half

I know this is primary school level but I am trying to speed up my mental arithmetic skills.

If in some calculation I get say 99.5 and I need to divide by two. Is it quickest to just do the long division as in

4 9 . 7 5
-----------
2 | 9 9 . 5
8
-
1 9
1 8
----
1 5
1 4
-------
1 0


Or are there any tricks?

I thought about half of 100 is 50. But value is only 99.5 so I take a quarter off. but that does seem fraught with error.

Anyone have any suggestions on the speediest and least error prone way to tackle such mental sums?
Original post by acomber
I know this is primary school level but I am trying to speed up my mental arithmetic skills.

If in some calculation I get say 99.5 and I need to divide by two. Is it quickest to just do the long division as in

4 9 . 7 5
-----------
2 | 9 9 . 5
8
-
1 9
1 8
----
1 5
1 4
-------
1 0


Or are there any tricks?

I thought about half of 100 is 50. But value is only 99.5 so I take a quarter off. but that does seem fraught with error.

Anyone have any suggestions on the speediest and least error prone way to tackle such mental sums?


I tend to think of integers separately, decimals seperately and then add them together.

So half of 99 is 48.5, half of 0.5 is .25, add then together is 49.75

Another way you could think of it is by timings the number by 2 and dividing by 4 :smile:
(edited 9 years ago)
Original post by Slowbro93
I tend to think of integers separately, decimals seperately and then add them together.

So half of 99 is 48.5, half of 0.5 is .25, add then together is 48.75

Another way you could think of it is by timings the number by 2 and dividing by 4 :smile:


Pretty much what I did except half of 99 is 49.5 :wink:
Half of 99 is 49.5

Half of 0.5 is 0.25

44.5+0.25=49.75
Reply 4
Avatar for acomber
acomber
OP
11
I think you meant half of 99 is 49.5???

I like that idea. I will use. Thanks.

Original post by Slowbro93
I tend to think of integers separately, decimals seperately and then add them together.

So half of 99 is 48.5, half of 0.5 is .25, add then together is 48.75

Another way you could think of it is by timings the number by 2 and dividing by 4 :smile:
99.5 is 0.5 less than 100, so the solution is 0.25 less than 50; 49.75
Original post by Guitarded
Pretty much what I did except half of 99 is 49.5 :wink:



Original post by acomber
I think you meant half of 99 is 49.5???

I like that idea. I will use. Thanks.


Typo :facepalm2:

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