Math Is Fun Forum

ryan_lang

Guest

mental maths

Hi,

I needed some help trying to solve basic mental maths problems. They are usually in multiple choice answers and I tend to work backwards going through all the answers to see which is the right one.. where I really want to improve on time. So how would I solve some questions like:

160 - ? + 170 = 280

120 / ? + 7 = 11

can you solve these like equations? whats the best way to tackle problems like these? more examples whould be helpful..Thanks

Thank you :)

almost there

Member

Registered: 2009-11-11

Posts: 21

Re: mental maths

You did not mention a course you were taking or a specific source of these exercises, so I do not know what mathematical tools you have available to work with but I think I can offer some suggestions based on the nature of the exercises and that you refer to these as "mental maths" problems.

Yes, you can solve these exactly like equations. In fact, that's exactly what they are--equations with one unknown/variable. If you want to improve on time, you will be faster the more familiar you are with simple calculations. Look online or in basic arithmetic texts for some practice problem sets with single-operation exercises. Practice with exercises of addition and subtraction of 2-digit and 3-digit numbers, and memorization of multiplication tables will help you become very quick at these mental arithmetic problems. At this link (http://www.math.com/students/practice.html) there is a list of math topics for practice. If you click on "Basic Math", you can pick operations and numbers from 0-12 and it will make problems for you and time you to see how many you can do in one minute.  Search for other sites too, there are a lot of them out there.

Practice factoring numbers (which will become easier the more multiplication tables you know) will also help. Also, try doing a lot of your mental maths problems with pencil and paper. Doing this kind of practice will train you to be able to do the problems in your head.

Good luck!

Hi,

I needed some help trying to solve basic mental maths problems. They are usually in multiple choice answers and I tend to work backwards going through all the answers to see which is the right one.. where I really want to improve on time. So how would I solve some questions like:

160 - ? + 170 = 280

120 / ? + 7 = 11

can you solve these like equations? whats the best way to tackle problems like these? more examples whould be helpful..Thanks

Thank you

nicol3

Member

Registered: 2009-11-24

Posts: 4

Re: mental maths

the beast way i know is +160and 170 =330-280=50 that is how i do my math here r som more.
            670+700-?=800
              590-40+?=900

ryan_lang

Guest

Re: mental maths

You did not mention a course you were taking or a specific source of these exercises, so I do not know what mathematical tools you have available to work with but I think I can offer some suggestions based on the nature of the exercises and that you refer to these as "mental maths" problems.

Yes, you can solve these exactly like equations. In fact, that's exactly what they are--equations with one unknown/variable. If you want to improve on time, you will be faster the more familiar you are with simple calculations. Look online or in basic arithmetic texts for some practice problem sets with single-operation exercises. Practice with exercises of addition and subtraction of 2-digit and 3-digit numbers, and memorization of multiplication tables will help you become very quick at these mental arithmetic problems. At this link (http://www.math.com/students/practice.html) there is a list of math topics for practice. If you click on "Basic Math", you can pick operations and numbers from 0-12 and it will make problems for you and time you to see how many you can do in one minute.  Search for other sites too, there are a lot of them out there.

Practice factoring numbers (which will become easier the more multiplication tables you know) will also help. Also, try doing a lot of your mental maths problems with pencil and paper. Doing this kind of practice will train you to be able to do the problems in your head.

Good luck!

Thank you for your reply :)

I have been doing what you told me and have found some very useful websites applications and even some game app on the iphone :P

I just got confused with the minus sign on the first example so: (I changed the '?' to 'A' to make less confusing)

- A = 280 - 170 - 160

- A = -50

A = 50

The bit I was getting stuck on was taking away a minus number as I always use a table form to take away:
280
170-
___
110

110
160-
___
??? <---- how do you work out this without swapping the values around.. or is the swapping the only way using this table form?

Although this example is quite a simple one and could really be done in head :P

Okay second question:
12 / A + 7 = 11
How would I rearrange this to get A?

Thank you :)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: mental maths

Hi ryan_lang;

12 / A + 7 = 11
How would I rearrange this to get A?

12 / A + 7 = 11

Subtract 7 from both sides:

12 / A  = 4

Times both sides by A

12 = 4 A

Divide both sides by 4

12 / 4 = A

3 = A or A = 3

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
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