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January 24, 2015

January 24, 2015

Posted by **Sara** on Thursday, January 2, 2014 at 11:38pm.

- Elementary Math -
**Steve**, Friday, January 3, 2014 at 12:08ammultiply by 0.7

15.4 * 0.7 = 10.8

- Elementary Math -
**Sara**, Friday, January 3, 2014 at 12:18amI had her do an exact 15.4 x .7 and came up with 10.78. Just wanted to show her that this was the correct way of doing this problem. She didn't believe me :) Thanks for your help and confirmation

- Elementary Math -
**Steve**, Friday, January 3, 2014 at 5:33amYou are correct. Any time you need to divide, you can always multiply by the reciprocal.

That is, dividing by 2 is the same as multiplying by 1/2 (or 0.5)

In this case, I'm surprised that the question of division even arose, since you knew how many miles you could go on 1 gallon of gas. For any other number of gallons, just multiply by that number to get the miles.

Not to confuse the issue, but you can keep the units of measure with the numbers. That is if you want to convert gallons to miles, you need a conversion factor.

in this case we have 15.4 mi/1 gal.

So, to convert gallons to miles, you just multiply by the conversion factor and the units cancel, just like any other factor.

.7 gal * (15.4mi/1gal) = 10.78 mi

You can always multiply by 1 without changing anything. A conversion factor is just a way of writing "1" that includes units. The goal is to make the old units cancel out, leaving the new, desired, units.

So, it's just like converting seconds to hours.

100 sec * (1 hr/3600 sec) = 1/36 hr

.3 hr * (3600 sec/1 hr) = 1080 sec

- Elementary Math -
**Jamie**, Tuesday, January 13, 2015 at 5:54pmI just told my little boy to do 15.4 x .7 and he got 10.78

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