Question

Which of the following is not true?

Answer 1

Correct option is C. $$7+8\times 9=(7+8)\times (7+9)$$
$$\textbf{Step 1: Recall Associative property of addition and multiplication.}$$

By Associative property of addition and multiplication we have

$$(7 + 8) + 9 = 7 + (8 + 9) $$ and $$(7 \times 8) \times 9 = 7 \times (8 \times 9)$$ are correct

$$\therefore\ \textbf{Option A and B are true}$$.

$$\textbf{Step 2: Recall Distributive property of multiplication over addition}$$

By distributive property of multiplication over addition we have

$$7 \times (8 + 9) = (7 \times 8) + (7 \times 9)$$ is correct.

$$\textbf{So Option D is also true}$$.

$$7 + 8 \times 9 = 7 + 72$$

$$ = 79$$

$$(7 + 8) \times (7 + 9) = 15 \times 17$$

$$= 255$$

So $$7 + 8 \times 9 = (7 + 8) \times (7 + 9)$$ is incorrect.

$$\therefore\ \textbf{Option C is not true}$$.

$$\textbf{Therefore the correct option is C}$$.