blog.thembid.com— Sometimes its very useful to be able to perform math calculation mentally and fast. This article lists five easy methods you can apply right away.
Jul 14, 2007View in Crawl 4
Subtract a number from 1000, 30000, 500000 or any number which end with zeros:For example, 1000 - 359. 1. Instead of calculating 1000 - 359, make it 999 - 359 + 1.2. Calculate the first part, it would be easy to work out to be 640.3. So the final answer is 641. This trick works very well in supermarket (among many places), but it's surprising that quite a lot of people don't know it.
Do Math Quickly in Your HeadSome time ago a picked up a cool little book called ?Short-Cut Math? by Gerard W. Kelly. It?s promise was to increase my calculation ability (in my head) up to three times. Following are the tips that stayed with me since I read the book and that I found most useful. Now I use these techniques when dealing with our startup ThemBid.com when I?m negotiating over license agreements on the fly during lunch meetings.1. Round Off to a Quick ApproximationFirst determine a level of accuracy you are happy with, then round the numbers appropriately before making the calculation. This is also useful to determine a quick ballpark figure before doing the actual calculation.2. Break Up Into PartsSay you have to multiply 613 by three. Try multiplying first 600 by 3, then 10 by 3 then 3 by 3 and adding the results.3. Omit WordsWhen calculating in your head, think of the results rather than saying out the words. For example to compute 30/2, just think 15 instead of thirty divided by two equals fifiteen.4. Quickly Find Three Common Percentages20% -> Divide the number by 533.3% -> Divide the number by 350% -> Divide the number by 25. Finding Percentages by Using 100?sThe percentage of a hundred is the percentage number itself. For example, 15% of 100 is 15. Use this, combined with the Break Up Into Parts method.The book has many more math shortcuts, but these are the ones that stuck to memory and I find myself using regularly. Have you learned any math shortcuts that allow you to quickly perform calculations in your head?
Closed AccountJul 15, 2007
That's a pretty good rule. 18% is a fair compromise between 20% and 15%
meatmcguffinJul 16, 2007
Ah, i guess you don't need that sort of system when the tax doesn't vary across the entire country. Thanks!
mothrogJul 16, 2007
Tips are there to ensure proper service. You aren't entitled to a given percentage of the bill, you earn it. If you don't like that, find another job.
resplenceJul 16, 2007
Where I live the usual amount is 10%, but it's entirely optional; choosing not to leave anything is not even frowned upon.
changyang1230Jul 17, 2007
Subtract a number from 1000, 30000, 500000 or any number which end with zeros:For example, 1000 - 359. 1. Instead of calculating 1000 - 359, make it 999 - 359 + 1.2. Calculate the first part, it would be easy to work out to be 640.3. So the final answer is 641. This trick works very well in supermarket (among many places), but it's surprising that quite a lot of people don't know it.
karthickdossJul 19, 2007
Do Math Quickly in Your HeadSome time ago a picked up a cool little book called ?Short-Cut Math? by Gerard W. Kelly. It?s promise was to increase my calculation ability (in my head) up to three times. Following are the tips that stayed with me since I read the book and that I found most useful. Now I use these techniques when dealing with our startup ThemBid.com when I?m negotiating over license agreements on the fly during lunch meetings.1. Round Off to a Quick ApproximationFirst determine a level of accuracy you are happy with, then round the numbers appropriately before making the calculation. This is also useful to determine a quick ballpark figure before doing the actual calculation.2. Break Up Into PartsSay you have to multiply 613 by three. Try multiplying first 600 by 3, then 10 by 3 then 3 by 3 and adding the results.3. Omit WordsWhen calculating in your head, think of the results rather than saying out the words. For example to compute 30/2, just think 15 instead of thirty divided by two equals fifiteen.4. Quickly Find Three Common Percentages20% -> Divide the number by 533.3% -> Divide the number by 350% -> Divide the number by 25. Finding Percentages by Using 100?sThe percentage of a hundred is the percentage number itself. For example, 15% of 100 is 15. Use this, combined with the Break Up Into Parts method.The book has many more math shortcuts, but these are the ones that stuck to memory and I find myself using regularly. Have you learned any math shortcuts that allow you to quickly perform calculations in your head?
amishbhavsarOct 20, 2008
Checkout www.LazyMaths.com to see the best collection of Mental Math shortcuts