# Forming expressions

• Apr 21st 2010, 01:20 AM
Natasha1
Forming expressions

There are 20 coins in Sam's money box.

There are n 50p coins and the rest are 10p coins.

1) Write down in terms of n the value of all the 50p coins

I put 50n

2) Write down in terms of n the value of all the 10p coins

Not too sure? Is it 50n + 10????

3) Write down in terms of n the value of all 20 coins.

Not too sure?

4) Write down in terms of n the number of 10p coins in Sam's money box?

I put 20 - 50n is this correct?

5) The total of all coins in Sam's money box is £5.20
Write down an equation to express this information and solve it to find the value of n?

6) Hence fidn the total of the 10p coins in Sam's money box?
• Apr 21st 2010, 01:34 AM
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Quote:

Originally Posted by Natasha1

There are 20 coins in Sam's money box.

There are n 50p coins and the rest are 10p coins.

1) Write down in terms of n the value of all the 50p coins

I put 50n

2) Write down in terms of n the value of all the 10p coins

Not too sure? Is it 50n + 10????

3) Write down in terms of n the value of all 20 coins.

Not too sure?

4) Write down in terms of n the number of 10p coins in Sam's money box?

I put 20 - 50n is this correct?

5) The total of all coins in Sam's money box is £5.20
Write down an equation to express this information and solve it to find the value of n?

6) Hence fidn the total of the 10p coins in Sam's money box?

For 2) you can assign a new variable name for the 10p coins, say, k.

Then n + k = 20

So k = 20 - n

So the value of the 10p coins is 10k = 10(20-n) = 200-10n

3)

50n + 10k = ?

4)

I did this as part of 2). Your answer is not correct.

5)

Use your equation from 3) and set it equal to 520.

6)

Use the equation from 4) to find k given n.

One last note: Depending on your teacher, you might want to be careful to include units in your answers, in this case, pence.
• Apr 21st 2010, 02:26 AM
Natasha1
I can't use a new variable though, it says it in the question
• Apr 21st 2010, 02:34 AM
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Quote:

Originally Posted by Natasha1
I can't use a new variable though, it says it in the question

You misunderstand me.

The new variable k is used to keep track of things, to help us manipulate the numbers. The answers are still given only in terms of n, when asked for.
• Apr 21st 2010, 02:41 AM
Natasha1
I understand. It's only that for question 3 you said it in terms of n and k. When it asks only in terms of n
• Apr 21st 2010, 03:17 AM
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Quote:

Originally Posted by Natasha1
I understand. It's only that for question 3 you said it in terms of n and k. When it asks only in terms of n

Okay, there's a little misunderstanding here but not too bad.

When I wrote

"50n + 10k = ?"

I meant for you to replace the question mark according to

10k = 10(20-n) = 200-10n

It looks like this:

50n + 10k = 50n + 200 - 10n

= 40n + 200

Clear now?