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8-56. Find each sum or difference without a calculator.

1. $\frac { 7 } { 10 } + \frac { 2 } { 3 }$

2. 0.9 – 0.04

3. $3 \frac { 1 } { 4 } + 2 \frac { 11 } { 12 }$

4. $14 \frac { 1 } { 3 } - 9 \frac { 1 } { 5 }$

For part (a), review the Math Notes box below to find help with adding fractions.

To add the fractions together, we can start by finding the least common multiple of 3 and 10 so we can use that number as a common denominator. This table lists multiples of 3 and 10.

$\left. \begin{array} { | c | c | c | c | c | c | c | } \hline 3 & { 6 } & { 9 } & { 12 } & { 15 } & { 18 } & { 21 } & { 24 } & { 27 } & { 30 } & { 33 } \\ \hline 10 & { 20 } & { 30 } & { 40 } & { 50 } & { 60 } & { 70 } & { 80 } & { 90 } & { 100 } & { 110 } \\ \hline \end{array} \right.$

LCM is 30. We can rewrite each fraction to have a denominator of 30 by using Giant Ones, as shown below. Can you add the fractions now? $\frac{41}{30}\text{ or }1\frac{11}{30}$

Whenever adding or subtracting decimals, be sure to line up the decimal point! It may help to write this problem like this:

$\:\:\:\:0.90\:$

$\underline{-0.04\:}$

$\:\:\:\:?.??\:$

Also, remember that the decimal point will fall in the same place in your answer. Refer to the Math Notes box below.

Refer to the Math Notes box below. 