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# Algebra: expressing relations : Post 16 Level 2 : Mathematics Content Knowledge

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Post 16 Level 2
Algebra: expressing relations
Question 1 of 27

# 1. How confident are you that you can identify variables and relations in familiar and unfamiliar situations within and outside mathematics?

## Problem

Two households are on the same electricity tariff. Their monthly electricity bill is calculated by using the formula

C = S + (U × N)
Where C is their monthly bill
S is the standing charge
U is the unit cost per kilowatt-hour
N is the number of units used

Which of C, S , U and N would be different for each household?

Prompt 1.

They are on the same tariff so their standing charge would be the same.

Prompt 2.

They are on the same tariff so the cost per unit of electricity used would be the same.

## Solution

C and N

Because they are on the same tariff the only thing that could be different for each household is the number of units of electricity they use (N) and hence the total cost of electricity for that month (C).

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