Question # 17

Thursday, November 26, 2009
Hi guys! So the question is:

To calculate -3/4 +(-2/ 3), Amy decided to convert the fractions to decimals and convert the decimals on a scientific calculator.
a) Explain why she had difficulty in determining the the exact answer by this method.
b) How should she calculate to get an exact answer?

a) -2/3 is a repeating decimal. That would mean she would have to round off to add the fractions together, which would not give her an exact answer. Although she could still find the decimal equivalent for -1 5/12. To do that, she would have to divide -5 by 12, and add that to -1.

-1 + (-0.41666.....) = -1.4167 (answer has been rounded)

I still wouldn't advise using this method because 5/12 is a repeating fraction, meaning we would have to round off, which would not give her an exact answer.

b) She should have just added the fractions together.
-3/4 + (-2/3) = -9/12 + (-8/12)
= -17/12
= -1 5/12

Since this fractions cannot be simplified further, we are done. Well, I think that explains everything. If you have any questions or something is wrong, or if you just want to COMMENT, please do. Thanks for reading! :)

3 comments:

Mr. B. said...

Kristin. Could Amy have have found a decimal equivalent for -1 5/12? If so how? Is it exact?

shaneille 9-05 said...

KRISTEN! WHY IS EVERYTHING SO BIG! Anyways Great Job, short post, but it was a short question. You explaned everything, but no picture... :(

Aleiah 905 said...

Good job Kristin, I understood what you said. It was easy to understand.

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