Loft insulation reduces annual heating costs by 20%. after he insulated his loft, curtley's annual heating cost was £520. work out curtley's annual heating cost would have been if he had not insulated his loft. (if you know how to work it out can you show your workings)

Without isolation annual cost would be 650$

Step-by-step explanation:

Without isolation annual cost is named x and it's worth 100%

With isolation annual cost is 520$ and it's worth (100%-20%) = 80%

Now we will make proportion

x : 520 = 100 : 80

When we multiply external and internal members we get

80 x = 100 · 520 => x = 100 · 520/80 = 650$

x = 650$

God with you!!!