Answer:
0.7262
Step-by-step explanation:
Let random variable = X
Probability of getting a cookie with at least 55 chips:
P(55≤ X ≤78), where X1 = 55 and X2 = 78
Let mean, U = 66 and standard deviation, S.D. = 10
Let Z = X - U/S.D; Z1 = X1 - U/S.D and Z2 = X2 - U/S.D
Z1 = 55 - 66/10 = - 1.1
Z2 = 78 - 66/10 = 1.2
P(X1≤ X ≤ X2) = P(X1 -U/S.D ≤ X - U/S.D ≤ X2 - U/S.D)
P(Z1 ≤ Z ≤ Z2) = P(0 ≤ Z ≤ Z1) + P(0 ≤ Z ≤ Z2)
Hence, (55 ≤ X ≤ 78) = P( - 1.1 ≤ Z ≤ 1.2)
∴ P(-1.1 ≤ Z ≤ 1.2) = P(0 ≤ Z ≤ 1.1) + (0 ≤ Z ≤ 1.2)
= 0.3413 + 0.3849 = 0.7262
