I would say option 3 hopefully im right!!
Answer:
a

b

Step-by-step explanation:
From the question we are told that
The mean value is 
The standard deviation is 
Considering question a
The sample size is n = 9
Generally the standard error of the mean is mathematically represented as

=>
=> 
Generally the probability that the sample mean hardness for a random sample of 9 pins is at least 51 is mathematically represented as



=> 
From the z table the area under the normal curve to the left corresponding to 2.5 is

=> 
=> 
Considering question b
The sample size is n = 40
Generally the standard error of the mean is mathematically represented as

=>
=> 
Generally the (approximate) probability that the sample mean hardness for a random sample of 40 pins is at least 51 is mathematically represented as

=> 
=> 
From the z table the area under the normal curve to the left corresponding to 5.2715 and
=> 
So

=> 
I think it’s 37 sandwiches if he only sold sandwiches
Answer: 16590
Step-by-step explanation:
The formula we use to find the sample size is given by :-
, where p = prior estimate of population proportion.
= Critical z-value (Two- tailed)
E= Margin of error .
Let p be the population proportion of cyanobacteria.
Given : E = 0.01
Critical value for 99% confidence interval : 
If Ian does not want to rely on previous knowledge , then we assume p=0.5 because the largest standard error is at p=0.5.
Now, the required sample size = 

Required sample size = 16590
The best way too solve it is to cross multiply. When you get the answer tell me and I’ll check it