Quickly Dividing in TwoDate: 7/8/96 at 8:39:27 From: Anonymous Subject: Quickly Dividing in Two I work in a store where everything is half price. Are there any quick tricks for figuring out fifty percent of a number such as 14.95 in ones head? Date: 7/8/96 at 12:33:44 From: Doctor Jodi Subject: Re: Quickly Dividing in Two Hi there! I'm not sure if this is a "quick trick" or not, but here are several ideas. Some are variations on the same theme: - round UP to the nearest whole number, which is 15 - divide by two (to get 15/2 or 7.50) - now subtract 15 - 14.95, to get .05 - divide .05 by two (to get .025) and subtract this from 7.50 to get 7.475 (the store will probably round it to 7.48) Another idea: - round DOWN to the nearest whole number, which is 14 - divide by two (to get 7) - now subtract 14.95 - 14 to get .95 - divide .95 by two to get .475 and add this to 7 to get 7.475 (the store will probably call this 7.48) Those methods recalled that 50 percent is also 1/2. You can also use the fact that 50 percent is the same as 10 percent times 5: Since 10 percent is the same as 10/100 or 1/10, first divide by ten (which amounts to moving the decimal point): - divide by ten to get 14.95/10, which is 1.495 - now multiply by five to get 7.475 and round to 7.48 You can also combine variations on the methods above (like multiplying 1.5 by 5 and then subtracting .005 times 5). I'm not sure these are the best methods, but I use them regularly. I hope they help. Let us know if you think of any other ways to do this in your head. -Doctor Jodi, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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