"It is generally believed that electrical problems affect about 14% of new cars. An automobile mechanic conducts diagnostic tests on 128 new cars on...

"It is generally believed that electrical problems affect about 14% of new cars. An automobile mechanic conducts diagnostic tests on 128 new cars on the lot." Q1 = What is the standard deviation for the sample proportion? a.) 0.11 b.) 0.021 c.)0.031 d.) .021 My solution was c) 0.031 Next question was "What is the probablily that in this group over 18% of the new cars will be found to have electrical problems?"I'm asking if I'm on the right track looking at the z-score? I'm drowning. Thanks for any help!