Thursday

January 29, 2015

January 29, 2015

Posted by **Sindy** on Friday, February 1, 2008 at 1:36am.

1. For a quick way of doing multiplication, you can do:

for example: 81 x 89=? First you do 1x9=9 in which case you have to add '0' in front of it to make it 09. Then you add 1 to any of the 8s and multiply the tens digits making 72. You add the digits 72 to 09 making 7209.

Another one: 64x66=? 6x4= 24 and 6+1=7. Then I go 6x7=42. So the digits 42 and 24 makes 4224.

The question is WHEN can I do this. I already know that the last 2 digits must add up to 10, but what number does this method end? Over 100?

Second question. Why does 9+4=1? Because of clock arithmetic. 9o'clock + 4 hours= 1 o'clock, and the modulus is 12 for 12 hours for one cycle. I need to find out what other things uses a particular modulus. I've managed to think of a month(31,30,29,28) days.

What else?

Thanks heaps!

- URGENT MATHS -
**Writeacher**, Friday, February 1, 2008 at 7:34amA math teacher will have to help you with your first question, but here are some ideas for your second one:

http://www.unc.edu/~rowlett/units/custom.html

16 ounces = 1 pint

2 pints = 1 quart

4 quarts = 1 gallon

etc.

inches, feet, yards, miles...

**Answer this Question**

**Related Questions**

finance /accounting- PLEASE HELP - Aging Accounts Receivable: Madariaga Campany'...

chemistry - The disintegration of a radioisotope, such as I-131 to Xe-131, is ...

urgent urgent algebra - find the composite function fog f(X) = 1/X-5,g(x)-6/x ...

Criminal justice - Can someone please help. Who is responsible for the concept ...

Math - Ansgar is writing a novel. He writes seven days a week. On each of those ...

maths - 300 men were engaged to complete a job in a certain number of days. but ...

math - of the following which is the closest approximation to the amount of time...

Algebra - Two different radioactive isotopes decay to 10% of their respective ...

time n work - a and b together can do a piece of work in16 days.b and c can do ...

math - Sam can do a job in 4 days that Lisa can do in 6 days and Tom can do in 2...