Mental Arithmetic Operation Please - urgent

maverik_

New member
Joined
Jun 10, 2013
Messages
6
Hello

I have been asked to solve the following type equation mentally:


2/6 * 9810


So two divided by six then times by 9810.

I have no clue how to solve this equation mentally.

I really need someone with excellent knowledge of maths to help me out here.

I have a mental arithmetic test coming up and I need some guidance if anyone is top at mental arithmetic and would be able to spend an hour or two on skype with me it would be highly appreciated.

Thanks

mh
 
Hello

I have been asked to solve the following type equation mentally:


2/6 * 9810


So two divided by six then times by 9810.

I have no clue how to solve this equation mentally.

I really need someone with excellent knowledge of maths to help me out here.

I have a mental arithmetic test coming up and I need some guidance if anyone is top at mental arithmetic and would be able to spend an hour or two on skype with me it would be highly appreciated.

Thanks

mh
The whole point of mental arithmetic is simplicity. You need to know the basic rules of arithmetic, such as that multiplying by 1/3 is the same as dividing by 3.

2/6 is exactly 1/3. I have no clue off the bat whether 9810 is evenly divisible by 3, but 9900 obviously is. Then I see that 9810 is 90 less than 9900, and 90 is also evenly divisible by 3 so the answer is 3300 - 30 = 3270. Notice that if all I "saw" was that 9810 was close to 9900, I'd have got an answer of 3300, which is correct within 1%.
 
Thanks, I got that now.

SO what do I do when something wont break down to the same as 1 /3 for example:

5/4 * 9654
 
Thanks, I got that now.

SO what do I do when something wont break down to the same as 1 /3 for example:

5/4 * 9654
5/4 * 9654 means that it is one quarter greater than 9654, which is close to 9600. One quarter of 9600 is 2400. 400 + 600 is 1000. So 9 + 2 + 1 = 12, or 12 thousand. It's not an exact answer, but mental arithmetic is about approximate answers.
 
Thanks, I got that now.

SO what do I do when something wont break down to the same as 1 /3 for example:

5/4 * 9654

The way I would do it (without calculator):

5/4 * 9654 = 10/8 * 9654 = 96540/8 =12067 + \(\displaystyle \frac{1}{2}\)
 
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