Lesson 3, Topic 3
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Solving Combined Products With Sums & Differences

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Example 1

Subtract the product of 9 and 40 from 450

Solution

You solve them in stages/steps

9 x 40 = 360

450 â€“ 360 = 90

Example 2

Add the negative difference between 27.9 and 35.7 to the product of 27.9 and 35.7

Solution

(27.9 x 35.7)  +  (27.9 – 35.7)

=   996.03 – 7.8

Ans = 988.23

Example 3

Find the difference between the product of $$\scriptsize 1 \frac{5}{8} \; and \; \frac{4}{5}$$ and the difference between $$\scriptsize 1 \frac{5}{8} \; and \; \frac{4}{5}$$

Solution

$$\left [ \scriptsize 1 \frac{5}{8} \: \times \; \frac{4}{5} \right] \: – \: \left[ \scriptsize 1 \frac{5}{8} \: – \: \frac{4}{5} \right] \\ \left [ \frac{13}{8} \: \times \: \frac{4}{5} \right] \: – \: \left[\frac{13}{8} \: – \: \frac{4}{5} \right]$$

$$\frac{13}{10} \: – \: \frac {65 \: – \: 32}{40} \\ = \frac{13}{10} \: – \: \frac{33}{40} \\ = \frac{ 52 \: – \: 33}{40} = \frac{19}{40}$$

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