The answer I get is not amoung the answers offered. I'd appreciate some help in telling me where I went wrong!!

In order to determine whether or not a particular medicine was effective in curing the common cold, one group of patients was given the medication, while another group received sugar pills. The results of the study are shown below.

/ Patients cured / Patients not cured

Received medication / 70 / 10

Received sugar pills / 20 / 50

We are interesting in determining whether or not the medication was effective in curing the common cold.

The test statistic is

a. 10.08

b. 54.02

c. 1.96

d. 1.645

This was my solution:

Hypothesis:

H0: p1 - p2 <= 0

Ha: p1 - p2 > 0

/ Group 1- med / Group 2- sugar pill

Sample size / 80 / 70

Response of interest / cured / cured

Count of response / 70 / 20

Sample proportion / 0.875 / 0.286

Hypothesized value 0

Point estimate difference 0.589

Pooled estimate of p 0.6

Standard error 0.080

Test statistic (z) 7.483 (my answer)

As you can see, my answer is not amoung those offered. Can anyone here please explain why?

Thanks for your help!!!