Question

How do you evaluate `20+ 5\times 9`?

Answer 1

`20 + 5xx9 = 65`

Explanation:

Given: `20 + 5xx9`

In math there are rules called "order of operations" or operator precedence.

Typically we start on the left and work our way to the right to simplify an expression.

Multiplication and division have priority over addition or subtraction.

To override the order of operations, parentheses and brackets can be used. The order of operations requires parentheses to be completed first.

This means `20 + 5xx9 = 20 + (5 xx 9) = 20 + 45 = 65`

Answer 2

`65`

Explanation:

Count the number of terms first - they are separated by `+ and -` signs.

There are two terms. Simply each to a single answer and these can be added in the last step.

`color(blue)(20) " "+" "color(red)(5xx9)`

`=color(blue)(20) " "+" "color(red)(45)`

`=65`

In simplifying an expression with several operations, in each term, the strongest operations of powers and roots have to be calculated first.
Then multiplication and division

Lastly addition and subtraction.

If this order is to be changed with a weaker operation being done first, it is shown in brackets.

Compare:

`20+5xx9 = 20+45 = 65`

and

`(20+5)xx9 = 25 xx 9 = 225`