mathfantasia

Jun 16, 2012, 09:15 AM

SO . . . wondering why the distributive property works? Want to average: 62, 63, 65, 67, 64, 68, 61, 64, 65, 65 in your head? Or maybe you're trying to quickly convert 1011001110 base 2 into octal.

Cool Math has these topics and more.

Here's a Freebie: Weighted Averages in Your Head. In a college class of 10 men and 15 women, the men scored an average of 87 and the women an average of 83. What is the average of the class?

The "classical" way: (10*87+15*83)/(10 + 15) = 84.6

The "cool" way: Subtract the lower test score from both test scores and take the weighted average. Then add back the lower test score to get the weighted average for the original problem.

In this problem: Subtract 83 from both averages. Men score 4 and women score 0. (4(10) + 0*15)/(10 + 15) = 40/25 which is 8/5 or 16/10 or 1.6. Add back the 83 and get 84.6

99 Cents at the moment.

http://itunes.apple.com/us/app/bsc-cool-math/id528528290?mt=8

Thanks for your support!

Cool Math has these topics and more.

Here's a Freebie: Weighted Averages in Your Head. In a college class of 10 men and 15 women, the men scored an average of 87 and the women an average of 83. What is the average of the class?

The "classical" way: (10*87+15*83)/(10 + 15) = 84.6

The "cool" way: Subtract the lower test score from both test scores and take the weighted average. Then add back the lower test score to get the weighted average for the original problem.

In this problem: Subtract 83 from both averages. Men score 4 and women score 0. (4(10) + 0*15)/(10 + 15) = 40/25 which is 8/5 or 16/10 or 1.6. Add back the 83 and get 84.6

99 Cents at the moment.

http://itunes.apple.com/us/app/bsc-cool-math/id528528290?mt=8

Thanks for your support!