1) It is estimated that the mean life span of oil-drilling bits is82hours. Suppose an oil exploration company purchases drill bits that have a life span that is approximately normally distributed with a mean equal to82hours and a standard deviation equal to 12 hours. (Round your answers to four decimal places.)

(a) What proportion of the company's drill bits will fail before67hours of use?

(b)What proportion will last at least67hours?

(c)What proportion will have to be replaced after more than97hours of use?

and also question 10.

MENDSTAT14 6.E.045. ASK YOUR TEACHER PRACTICE ANOTHER Are you helping to save the environment? A USA Today Snapshot found that about 78% of Americans believe that recycling trash makes the biggest difference in protecting the environment. 10. [14 Points] Survey respondents say recycling trash, reducing waste, and reusing materials make the biggest difference in protecting the environment. Suppose a random sample of n : 40 adults are polled and asked if they believed that recycling made the biggest difference in protecting our environment. Let us assume that the 78% figure is, in fact, correct. What are the probabilities for the following events? (Use the normal approximation. Round your answers to four decimal places.) (a) Fewer than 28 individuals believe that recycling makes the biggest difference? :I (b) More than 33 individuals believe that recycling makes the biggest difference? :I (c) More than 7 indiViduals believe that recycling does not make the biggest difference? :I