# Problem solving with mixed operations

Lesson

We've looked at the order of operations in Maths in Order. We can now use this process to solve problems that may involve things like money, weight and distance.

#### Examples

##### question 1

Evaluate: A jug holds $0.75$0.75l of juice. If I have $3$3 jugs, how many $250$250ml glasses can I fill?

Think: I want both units of capacity to be the same, so I am going to convert $0.75$0.75l to $750$750ml by multiplying it by $1000$1000.

Do: $750\times3=2250$750×3=2250ml

$2250\div250=9$2250÷​250=9

That means I can fill $9$9 glasses.

##### question 2

Evaluate: What is the difference between $187$187 and the product of $15$15 and $3$3?

Think: How do I write this as an equation so that the order of operations is correct?

Do:

 $187-\left(15\times3\right)$187−(15×3) $=$= $187-45$187−45 $=$= $142$142

##### Question 3

There were $139$139 sharks in Charon Bay last year. This year the population has decreased to $92$92 sharks.

How much of the shark population in Charon Bay was lost in the last year?

##### Question 4

I want to make $4$4 biscuits with $15$15 chocolate chips in each of them. How many chocolate chips do I need to use in total?

##### Question 5

On a certain island a species of hawk sustains itself by eating the local rabbits.

In the first survey of animals on the island, there were found to be $3$3 rabbits for every hawk. The latest survey shows that this is still the case, but that the rabbit population has grown to $153$153 individuals. How many hawks does the island now support?

### Outcomes

#### NA4-1

Use a range of multiplicative strategies when operating on whole numbers