- #1

songoku

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- Homework Statement
- Exam marks, X, have mean 70 and standard deviation 8.7. The marks need to be scaled using the formula Y = aX + b so that the scaled marks, Y, have mean 55 and standard deviation 6.96. Find the values of a and b

- Relevant Equations
- E(aX + b) = a.E(X) + b

Var(aX + b) = a^2 Var (X)

Var (Y) = a

(6.96)

a = ± 0.8

But the answer key states that the value of a is only 0.8

Why a = -0.8 is rejected? Thanks

^{2}. Var (X)(6.96)

^{2}= a^{2}. (8.7)^{2}a = ± 0.8

But the answer key states that the value of a is only 0.8

Why a = -0.8 is rejected? Thanks