problem-8.21
Assuming the phones are a random sample from the population of all
phones, this can be done with prop.test():
> prop.test(c(14,15),c(150,125),alt="less")
2-sample test for equality of proportions with
continuity correction
data: c(14, 15) out of c(150, 125)
X-squared = 0.2702, df = 1, p-value = 0.3016
alternative hypothesis: less
...