# Help me with math rules. 18÷9(2)=? A) 1 or B) 4 Please explain.

Feb 11, 2016

1

#### Explanation:

you will apply the BODMAS rule . so according to the rule we will first we will solve the bracket first which is 9(2)= 18 then after solving the bracket divide according to the rule and u will get 1 by dividing 18/18.. just remember BODMAS is Bracket Or Division Multiplication Addition Subtraction

Aug 3, 2016

#### Explanation:

There are 2 operations going on here - multiplication and division.

Either can be done first, but we have to know which is the multiply and which is the divide....

It can be written like this:

$18 \div 9 \times 2 = \frac{18 \times 2}{9} = \frac{36}{9} = 4$

Or

$\frac{{\cancel{18}}^{2} \times 2}{\cancel{9}} = 4$

This is NOT the same as

$18 \div \left(9 \times 2\right)$ which can be shown as $\frac{18}{2 \times 9} = \frac{18}{18} = 1$

Aug 3, 2016

$1$ or $4$

#### Explanation:

If you are using PEMDAS, BODMAS or BIDMAS in pure form, then what we have here is the same as:

$18 \div 9 \times 2$

This is evaluated left to right (since multiplication and division have the same priority). So we perform the division first to get:

$2 \times 2$

then the multiplication to get:

$4$

If you are not restricted to PEMDAS/BODMAS/BIDMAS, then there are at least a couple of justifications for performing the multiplication first:

• By juxtaposing $9$ and $\left(2\right)$, the writer intended to convey that $9 \left(2\right)$ should be treated as one term, like $9 a$ with $a = 2$.

• The obelus $\div$ is historically shorthand for dividing the whole expression on the left by the whole expression on the right.

If you understood the expression one of these ways then you would perform $9 \times 2$ first giving $18$, then evaluate $18 \div 18$ to get the value $1$

This is not "wrong".

The purpose of conventions like PEMDAS is to try and disambiguate such cases, but such conventions can result in counterintuitive results.

The bottom line is that the writer of the expression should either be specific about what conventions they are using or add parentheses to make it unambiguous.