A house increases by 25% to £80,000. Find what it was worth before the rise.

A 15% increase means that the £80,000 represents 115% of the original value.

Therefore what we do is:

£80,000=£125% divided by 125 

which gives us 

£640 = 1%

then we want to multiply by 100 to change this to what we get for 100%, which gets us to:

£64,000!

So the orginal price was £64,000.

We can check that this answer makes sense: we know that there is an increase so it makes sense to get an original value less than the increased value!

(Note: I like to illustate this method with the use of a diagram which I would be able to do on the whiteboard in session mode).