double glazing costs

the 'Warmsnug Double Glazing' task comes from the 'Language of Functions and Graphs' (Red Box) resources produced by the Shell Centre (1985) and is available in pdf form

this task has been developed by NRICH

two variables are initially involved
students can decide what these are likely to be

one of the pricings given is (intentionally) incorrect

NRICH provide a spreadsheet for this task that enables other (their version 1) and harder questions to be posed:

• two variables plus a fixed rate (their version 2)
• three variables (their version 3)

these are further examples of version 1 (i.e. just with two variables)