# Tutor profile: Reagan C.

## Questions

### Subject: SQL Programming

What is a left join?

A left join sends back every row from the table on the left side of the join statement that matches the criteria in the WHERE clause, even if there is no related data from the table on the right side of the join statement. Here is an example: Let's say that we have two tables, Person and House. We want to show data on individuals, including data on the house they own. We want to show data on each individual even if they don't own a house. We would use a left join with Person on the left side of the join statement and House on the right side of the join statement. Both tables would relate on Person.PersonID = House.OwnerID.

### Subject: Linear Algebra

If A = [ 74, 96, 35, 42 ] and X = [ 4 what would be y? 7 5 1]

y = A*X. This can be also written as (a1*x1) + (a2*x2) + (a3*x3) + (a4*x4). Therefore y = (74*4) + (96*7) + (35*5) + (42*1) = 1185

### Subject: Statistics

John's shipping company wants to know about how many packages a day they are shipping on average. They recorded the number of packages they shipped a day for fifty days. The sample average is 80.3 and the sample standard deviation is 10.5. What is the 95% confidence interval for the average number of packages shipped in a day?

The following formula is used to answer this question: (sample average) +- (z-score of critical value)( sample standard deviation / square root of observations) (80.3) += (1.96)( 10.5 / √50) = [77.39, 157.69]

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