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nov 03 s1

http://math.mdsalih.com/Data/Edexcel%20Mathematics/S1/S1%20Nov%2003.pdf

on question 2 of this paper, november 2003, can someone explain it please as haven't fully worked out how to do it. Don't normally have problems on s1, and the mark scheme answer makes no sense. ty
Reply 1
Avatar for Chewwy
Chewwy
17
i) 0.6^3, easy enough

ii)
points: 0 10 20 30
p(x=X) 0.4, 0.6*0.4 0.6^2*0.4 0.6^3

iii)
mean = 0*0.4 + 10*0.6*0.4 + 20*0.6^2*0.4 + 30*0.6^3 = 11.76
s = rt(Var(x)) = SUMx^2 p(x) - mean^2 = do it yourself

iv) p(more second time) = p(more first time) (if independant)
1 = p(more second time) + p(more first time) + p(same)

p(more seond time) = (1-p(same))/2 = (1 - square of the probabilties lsited above)/2
Reply 2
Avatar for mathsdave
mathsdave
OP
thanks. think i get it now
(sorry should have specified it was the only the last part which was confused about)

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