The variables x and y are related so that when lgy is plotted against lgx a straight line passing through the points (4, 12) and (6, 17) is obtained. [Figure 7.1]
- (i)Express y in terms of x, giving your answer in the form y = axᵇ.[6]
- (ii)Find the value of x when y = 300.[2]
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Mark scheme
Marking points from the official mark scheme (May/June 2011). The mark or mark type is shown in brackets.
- [1] (i) m = 2.5
- [1] (i) c = 2
- [1] (i) lgy = 2.5lgx + 2
- [1] (i) 2 = lg100 or lg10²
- [1] (i) 2.5lgx = lg x^2.5
- [1] (i) y = 100 x^2.5
- [1] (ii) Solve 2.5lgx = lg3 or x^2.5 = 3 correctly
- [1] (ii) 1.55
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