Answer: He sold 10 pounds of cashews .
Step-by-step explanation:
Since we have given that
Selling price of walnuts = $4.00 a pound
Selling price of cashews = $7.00 a pound
Number of pounds of walnuts = 10
Let number of pounds of cashew be x
Total price at which he sold a mixture = $5.50
According to question,

Hence, he sold 10 pounds of cashews .
We need to test the hypotheses:

The
confidence interval for proportion is
.
Here 
The z value to be used is 1.96.
The 95% CI is
.
Since 0.5 lies in the interval (0.488,0.543), we cannot reject the null hypothesis with 95% confidence.
The most it can be seated is 16 because of the value of 4 with 4 different odds 4*4 =16