Help with calculation of a z-score

[altitus]

The question is: The producers of a new toothpaste claim that is prevents more cavities than other toothpaste brands. In other words, those who use the new toothpaste should have fewer cavities than those who used other brands. A random sample of 60 people use the new toothpaste for 6 months. The mean number of cavities at their next checkup is 1.5 The mean number of cavities in the general population (people who did not use the new brand of toothpaste), is 1.73. The standard deviation for this problem is 1.12.

The homework question that i need to find the answer to is: Decide whether to use a z test or a t test. Then find the z obtained or t obtained.

I'm pretty sure this problem requires the use of a z test, but I cannot figure out z obtained (z score). I desperately seek anyone's help who can understand what is needed to find the answer. Thank you so very much.

 

[tkhunny]

Okay, it's a Z-Score., A Z-score is a number of standard deviations.

How different are the results? How many standard deviations is that?

 

[altitus]

Okay, it's a Z-Score., A Z-score is a number of standard deviations.

How different are the results? How many standard deviations is that?

Thanks for the response... the information given in the word problem is all that is provided. The standard deviation given is 1.12. If you're asking me this because you want me to respond, my response to the question is that the difference between the two results, meaning the two means, is .23. I don't know if that's what you're asking... I'm so sorry... But the problem does have a multiple choice answer. The options are:

-1.675
+1.5
-1.643
+2.643

I just don't understand how to arrive at one of those answers, or even what the correct answer is. I've used the formula for calculation of z score, and I cannot come up with something close to one of those results.