17. To calculate -3/4 + (-2/3), Amy decided to convert the fractions to decimals and add the decimals on a scientific calculator.
a) Explain why she had difficulty in determining the exact answer by this method.
For Amy's method, she wanted to turn - 3/4 and -2/3 into decimals and just add them up.
If you convert - 3/4 into a decimal it would be - 0.75.
If you convert - 2/3 into a decimal it would be -0.6 repeating.
If you add those two up you can't get the exact answer because there is a repeating decimal in the question.
b) How should she calculate to get an exact answer?
Amy should just stick with adding it the fractions method.
- 3/4 + (-2/3)=
Well first you have to find the common denominator for the fraction. Their common denominator is 12. And how do you turn the denominator ( 4 ) and ( 3) to 12 ? You multiply 4 by 3 and you multiply the 3 by 4. Now the fractions denominator is 12. But you also have to do the same to both fractions numerator. So you multiply the 3 by 3 which is 9 and multiply the 2 by 4 which is 8. The fractions are now -9/12 and -8/12. Then you just add the 9 and 8 together and which becomes the numerator and the denominator stays the same.
a) Explain why she had difficulty in determining the exact answer by this method.
For Amy's method, she wanted to turn - 3/4 and -2/3 into decimals and just add them up.
If you convert - 3/4 into a decimal it would be - 0.75.
If you convert - 2/3 into a decimal it would be -0.6 repeating.
If you add those two up you can't get the exact answer because there is a repeating decimal in the question.
b) How should she calculate to get an exact answer?
Amy should just stick with adding it the fractions method.
- 3/4 + (-2/3)=
Well first you have to find the common denominator for the fraction. Their common denominator is 12. And how do you turn the denominator ( 4 ) and ( 3) to 12 ? You multiply 4 by 3 and you multiply the 3 by 4. Now the fractions denominator is 12. But you also have to do the same to both fractions numerator. So you multiply the 3 by 3 which is 9 and multiply the 2 by 4 which is 8. The fractions are now -9/12 and -8/12. Then you just add the 9 and 8 together and which becomes the numerator and the denominator stays the same.
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