A Kansas University research station wishes to investigate if a new variety of wheat is more resistant to a disease than an old variety. It is known that this disease strikes approximately 15% of all plants of the old variety. A field experiment was conducted, and of 120 new plants, 12 became infected.

Question

A Kansas University research station wishes to investigate if a new variety of wheat is more resistant to a disease than an old variety. It is known that this disease strikes approximately 15% of all plants of the old variety. A field experiment was conducted, and of 120 new plants, 12 became infected.
The calculated value of the test statistic is:

1.83
 		
1.10
 		
-1.53
 		
1.53
 		
1.83

MathGuru · Answer

You can try a proportional one-sample z-test for this one since this problem is using proportions.

Using a formula for a proportional one-sample z-test with your data included, we have:
z = .1 - .15 -->test value (12/120) is .1) minus population value (.15) divided by
√[(.15)(.85)/120] --> .85 represents 1-.15 and 120 is sample size.

Finish the calculation.