Question assuming sum of mother and father's age is 80

hence sd = 80

mean = 1288 Z = (X - mean)/sd = (X - 1288)/ 80

b)

P(X > 1250)

= 0.6826 c)

P(X > x) = 0.375
P(Z > z) = 0.375
z = 0.385
hence
x = mean + z* sd
= 1288 + 0.385 * 80
= 1318.8

d)
sd(Xbar) = sd(X) /sqrt(n)

P(Xbar < 1225)
= P(Z < (1225 - 1288)/(80/sqrt(200))
= P(Z < -11.1369)
= 0

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