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October 31, 2014

October 31, 2014

Posted by **Lecia** on Friday, January 7, 2011 at 8:16am.

10/21 or 15/28?

- approximation fractions -
**drwls**, Friday, January 7, 2011 at 9:13amOne way to answer would be to convert to common denominators.

10/21 = 40/84

15/28 = 45/84

so 15/28 is quite a bit larger.

Here is another way:

10/21 is 0.5/21 or 1/42 larger than 1/2

15/28 is 1/28 larger than 1/2.

Since 1/28 > 1/42, 15/28 is larger

- approximation fractions -
**bobpursley**, Friday, January 7, 2011 at 9:13amincrease the first by a factor of 28/21 or 4/3 or 1.3

10/21 * 1.3/1.3= 13/28

Which means 15/28 is the larger.

- approximation fractions -
**Reiny**, Friday, January 7, 2011 at 9:30amhere is yet another "very old-fashioned" way:

write the fractions side by side, and take the product of the "diagonals"

10/21 vs 15/28

diagonal leaning left = 10x28 = 280

diagonal leaning right = 21x15 = 315

since 280 < 315

10/21 < 15/28

- approximation fractions -
**drwls**, Friday, January 7, 2011 at 9:32amMy second method contained an error but got the right answer.

10/21 is 1/42 LESS than 1/2, not greater.

15/28 is greater than 1/2.

I should have seen that right away.

- approximation fractions -
**bobpursley**, Friday, January 7, 2011 at 9:55amhttp://www.echalk.co.uk/tasters/taster2/taster.html

A nice Texas estimating fractions exercise (Texas=UK)

- approximation fractions -
**Reiny**, Friday, January 7, 2011 at 10:42amnice!

(probably better than some of the "methods" used these days to teach fractions)

- approximation fractions -
**Damon**, Friday, January 7, 2011 at 3:47pmCool game !

- approximation fractions -
**Reiny**, Friday, January 7, 2011 at 7:24pmOH,MY Goodness

went to home page

http://www.echalk.co.uk/

The Blob Game is hilarious.

Catch what happens to the blob when you pick the wrong one.

**Answer this Question**

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