Write down the original price
original=£80 The overall percentage change is measured against this £80.
August: find the multiplier
100%+40%=140%=1.4 A 40% rise means multiplying by 1.4.
August: work out the price
£80×1.4=£112 The August price is £112.
October: find the multiplier
100%−30%=70%=0.7 A 30% fall means multiplying by 0.7.
October: apply it to the AUGUST price
£112×0.7=£78.40 The 30% comes off £112 (that is £33.60), not off the original £80. The October price is £78.40.
January: find the multiplier
100%−25%=75%=0.75 A further 25% fall means multiplying by 0.75.
January: apply it to the OCTOBER price
£78.40×0.75=£58.80 The January price is £58.80.
Multiply the three multipliers together
1.4×0.7×0.75 Successive percentage changes combine by multiplying their multipliers, never by adding the percentages.
Work out the product in stages
1.4×0.7=0.98,0.98×0.75=0.735 The single equivalent multiplier is 0.735.
Check the single multiplier against the price
£80×0.735=£58.80 The single multiplier gives the same January price. ✓
Compare the multiplier with 1
The multiplier is below 1, so the room is cheaper in January than it was originally.
Turn the multiplier into a percentage change
(0.735−1)×100=−26.5 The overall change is a 26.5% decrease.
Confirm from the prices
8080−58.80×100=8021.20×100=26.5% The price has fallen by £21.20, and £21.20 out of the original £80 is 26.5%. ✓
Watch the common error
+40%−30%−25%=−15%=−26.5% Adding the percentages gives a 15% fall, which is badly wrong. Notice too that +40% then −30% is not +10%: 1.4×0.7=0.98, already a 2% fall.
State the overall percentage change
26.5% decrease The January price is 26.5% below the original £80.