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.
She had difficulty in determining the exact answer because -2/3 is repeating decimal. However, -3/4 is terminating decimal. As a result she had to add -0.75 + (-0.6666...). Also she has to round the repeating decimal before adding on a scientific calculator but she may not know where to round it.
b) How should she calculate to get an exact number?
She should find the LCD of 3 and 4. Then change the fraction to be equivalent with the original fraction. Then, add the numerator but the denominator stays the same. Simplify.
(* What you do on the denominator you must do on the numerator.)