**This is where you have 2 equations but need to find out what the letters are. The letters are the same in both equations.**

**EG1) Three bottles of coke and 4 packs of crisps cost £4.20.**

Another day I buy 2 bottles of coke and 2 packs of crisps which cost £2.60.

How much would 3 packs of crisps cost?

Another day I buy 2 bottles of coke and 2 packs of crisps which cost £2.60.

How much would 3 packs of crisps cost?

**3b + 4c = £4.20**

2b + 2c = £2.60

2b + 2c = £2.60

**You need to get one of the letters amounts the same so they are balanced. If you times the whole bottom equation it will be balanced because there will be another 4c.**

**3b + 4c = £4.20**

4b + 4c + £5.20 (x2)

4b + 4c + £5.20 (x2)

**4b - 3b = b**

4c - 4c = 0

£5.20 - £4.20 = £1.00

b = £1.00

4c - 4c = 0

£5.20 - £4.20 = £1.00

b = £1.00

**£3.00 + 4c = £4.20**

£2.00 + 2c = £2.60

£2.00 + 2c = £2.60

**£4.20 = £3.00 = £1.20**

4c = £1.20

c = 30p

4c = £1.20

c = 30p

**1 pack of crisps is 30p.**

3 packs are 90p.

3 packs are 90p.