C- $1.89
a & b aren't enough and d is too much
Use the quadratic formula and a=4, b=3, c=-4
Answer: The percent higher is 41.68%. If 49 planes were selected, 20 of them should be above 15 years.
To find the percent, we first need the z-score.
(15 - 13.5) / 7.3 = 0.21
Now, use a normal distribution table to find the percent above a score of 0.21. It will be 41.68%.
To find the number of 49 planes above this value, multiply 49 by 0.4168. You will have about 20.4 planes.
Answer:
12.5
Step-by-step explanation:
see attached image