Question

a man moves to lie on an island in Europe. He has a choice of two water companies:
Manana Water: No standing charge. Pay £0.06 per m3 of water used.
Channel Water: Standing Charge: £30 every 3 months
£0.02 per m3 of water used
Special offer: 20% off your first bill.

he estimates that he uses 700m3 of water every 3 months. which company should he choose?

Answer 1

Manana would be the best choice in the long run—see all my work below.

Regular prices:

Manana: $700*.06=42$ £/3mos
Channel: $(700*.02)+30=44$ £/3mos

However, with the 20% discount on Channel Water, the first three months would look like:

(NOTE: This may be an overly complicated equation, but it's how it works out in my head.)

$(((\frac{700}{3})2*.02)+30)-((\frac{700*.02+30}{100})20)=30.53$ £ for the first three months.

Manana:
$4*42=168$ £/year

Channel:
$(2.75*44)+30.53=151.53$ £ for the first year, and $4*44=176$ £/year afterwards.