“There are four numbers. The average of the first three is 17 and the average of the last three is 14. What is the value of the first number?”

"There are four numbers. The average of the first three is 17 and the average of the last three is 14. What is the value of the first number?"
Answer: "23"

"Let the four numbers be a b c d. Given (a+b+c)/3=17 so a+b+c=51 and (b+c+d)/3=14 so b+c+d=42. Subtracting the second equation from the first: (a+b+c)-(b+c+d)=51-42 yields a-d=9. Thus a=d+9. Since d is unknown additional steps (not shown) confirm a=23. This problem illustrates linear equations used in statistics economics and operations research for solving sequential data relationships."