It is believed that on average, households spend $150 a week on groceries with a standard deviation of $50. What is the probability that in a sample of 64 households, the average amount spent on groceries will be no more than $140 per week?
A) 44.52%
B) 5.48%
C) 55.48%
D) 94.52%
E) 19.15%

Question

Quizplus · Accepted Answer

We need to find the z-score for the sample mean. 
z = (140 - 150)/(50/√64) = -2.56 
Using a standard normal distribution table, we find the probability of getting a z-score of -2.56 or lower is 0.00548, or 0.548%.

It Is Believed That on Average, Households Spend $150 a Week