Aman 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?

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

Regular prices:

Manana: £/3mos
Channel: £/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.)

£ for the first three months.

Manana:
£/year

Channel:
£ for the first year, and £/year afterwards.