Use the plan to prove the third angles theorem.
plan for proof: use the triangle sum theorem to show that the sums of the angle measures are equal. then use substitution to show angle c is congruent to angle f.

According to a study conducted in 2015, 18% of shoppers said that they prefer to buy generic instead of name-brand products. suppose that in a recent sample of 1500 shoppers, 315 stated that they prefer to buy generic instead of name-brand products. at a 5% significance level, can you conclude that the proportion of all shoppers who currently prefer to buy generic instead of name-brand products is higher than .18? use both the p-value and the critical-value approaches.