April 23, 2008 7:56pm CST
I have a hard time doing mental math. Does anyone have any tricks that make it easier/
• United States
24 Jul 08
Well, it depends on what kind of mental math you are doing. There are multitudes of tricks if you want to get started. (And the biggest "trick" is probably just practice.) This site has a lot of tricks for all sorts of numbers (two digit multiplication to squaring numbers ending in five and so on): http://mathforum.org/k12/mathtips/beatcalc.html Personally, I tend to stick to quick estimations using this method. Let's say you have two numbers you want to multiply, say 45×56. I would split either number into its tens and ones and distribute it into the other: (40+5)56 = 40×56+5×56 = 2240+280 = 2520 It's relatively easy to multiply 40 by 56 (it's just like multiplying a single digit number by a double digit one), so the answer comes faster. Or, to make it even easier: (40+5)(50+6) = 40×50+40×6+5×50+5×6 = 2000+240+250+30 = 2520. Don't you just love the parade of zeroes? Anyways, good luck. :]
13 May 09
You are right, movicont, practice is important and developing your own systems is better than trying to learn from others. In your example of 45 x 56 I would have calculated 56 x 50 and taken away 56 times 5(2800 - 280). The second amount comes easily because it has to be a tenth of the first calculation. It still gives the same answer of 2520 but of course I find my way easier to do because that is the way I am thinking.