Answer:


Step-by-step explanation:
Given
---- proportion of watches with defects
--- Number of watches
Solving (a): Represent at least 215 of 400 are defective
In inequalities, at least means: 
So, the probability is represented as: 
Solving (b): Calculate 
Normal or Poisson: Normal distribution is characterized by 2 parameters
and
.
These two parameters can be easily calculated from the given parameters in the question. So, we solve using normal distribution
Start by calculating the mean



Calculate standard deviation





By continuity correction, we have:



So, we have:

Calculating
, we have:

Calculate z score




So, we have:

Using the z score probability table, we have:

So, we have:

