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easy maths question

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easy maths question [#permalink] New post 06 Dec 2007, 09:00
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why does the cubic root of 0.000064 = 0.04

why does the square root of 0.04 = 0.2

I having difficultly in determining how many decimal place to move the answer after the cubic and sqaure roots are done, i.e. cubic root of 0.000064 = 0.04 and why not 0.004, etc.

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 [#permalink] New post 06 Dec 2007, 11:19
when you multiply a number by a decimal it gets smaller. 100 * .2 = 20

this is the same principal on a smaller scale. .2*.2 = 1/5 of .20 or .04
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 [#permalink] New post 06 Dec 2007, 19:59
gmat, first multiply as normal, then just count from tight to left the number spaces between the last digit of the number and the placement of the period to place the period:

In 7,654.321 you would have 3 spaces. In 4.3210123 you would have seven spaces.

To solve .4 x .4, first multiply: 16. Then count the number of spaces from right lo left (total is 2, one for each 4). Then you need to place he period on th product. Count from right to left the total number of spaces you counted before. Since the number is 2, you place the period 2 spaces from the right: .16

In your example:
.04*.04*.04 = 64, then you place the period six spaces to the left = .000064

Keep in mind that any number has a decimal period, although sometimes you do not need to represent it because:

2*2=4, now do the period (number of spaces to the left = 0) = 4.0

Hope this helps.
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 [#permalink] New post 07 Dec 2007, 01:53
when the decimals start getting long I take just a second to remember, .1 x .1 = .01, and so on. One tenth of one tenth. Each place to the right of the decimal point is reflected in the product.
  [#permalink] 07 Dec 2007, 01:53
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