Last year 10 percent of all teenagers purchased a new iPhone

Last year, 10 percent of all teenagers purchased a new iPhone. This year, a sample of 260 randomly chosen teenagers showed that 39 had purchased a new iPhone. The test statistic to find out whether the percent has risen would be

Solution

Formulating the null and alternatuve hypotheses,          
          
Ho:   p   <=   0.1
Ha:   p   >   0.1
As we see, the hypothesized po =   0.1      
Getting the point estimate of p, p^,          
          
p^ = x / n =    0.15      
          
Getting the standard error of p^, sp,          
          
sp = sqrt[po (1 - po)/n] =    0.01860521      
          
Getting the z statistic,          
          
z = (p^ - po)/sp =    2.687419249   [ANSWER]