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## Question

primary 5 | Maths
| Rate & Ratio

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spent

Bob's all money: 2u

Amos: u

Amos' all money: u+1800

spent

Bob's all money: 2u

Amos: 4u

Amos' all money: 4u+600

u+1800 = 4u+600

u = 400

Amos had $2200 ;

Bob had $800 at first

...

What we need to realise is that Bob spent all his money in both cases. So this amount doesn't change.

Letting Bob's money be 2 units makes calculation easier, as it can be divided by 2 and also multiplied by 2 to find the amount Amos spent in both cases.

2 units ÷ 2 = 1 unit

2 units x 2 = 4 units

Since Amos's total amount of money doesn't change, the difference in amount he spent equals the difference in amount he had left.

Difference = $1800 - $600 = $1200

$1200 more was spent on one case, so $1200 less remained at the end.

Difference also = 4 units - 1 unit = 3 units

So 3 units = $1200

1 unit = $1200 ÷ 3 = $400

A farmer has some chickens and ducks. If he sells 2 chickens and 3 ducks every day, there will be 50 chickens left when all the ducks have been sold. If he sells 3 chickens and 2 ducks every day, there will be 25 chickens left when all the ducks have been sold.

a) how many ducks are there?

b) how many chickens are there ?

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