Standard Scores and Z-Scores

Calculate a z-score using a given value and the corresponding mean and standard deviation.

The sales data for July and August of a frozen yogurt shop are approximately normal.

The mean daily sales for July was $270 with a standard deviation of $30.On the 15th of July, the shop sold $315 of yogurt.

The mean daily sales for August was $250 with a standard deviation of $25.On the 15th of August, the shop sold $300 of yogurt.

Which month had a higher z-score for sales on the 15th, and what is the value of that z-score?

• a.)
• July, with a z-score of 1.5.
• b.)
• August, with a z-score of 1.67.
• c.)
• July, with a z-score of 1.8.
• d.)
• August, with a z-score of 2.