A state has 20 cities. The train service in the state connects all cities in triplets; this means that one train shall circulate only among three particular cities. To ensure that any set of three cities in the state is interconnected through a triplet, what is the minimum number of trains needed?

On monday Rhonda made an average of 12 phone calls per hour for the first 6 calls she made , and then an average of 6 phone calls per hour for the remaining 6 calls she made. What was the average number of phone calls per hour that Rhonda made for the entire day

Last month a certain bookstore ordered a discount to preferred customers. After the fi…rst book purchased, preferred customers paid $12.99 for each additional hardback book purchased. If a preferred customer purchased a total of 4 hardback books and paid $21.95 for the fi…rst book, then the dollar amount that the customer paid for the 4 books is equivalent to which of the following?

John spent a total of $135 on baseball tickets. The price of a ticket is either $12 for the field seats or $5 for the balcony. What is the minimum amount of dollars he could have spent for the $12 tickets?

Tom is 10 years older than Carrie. However, 5 years ago Tom was twice as old as Carrie. How old is Carrie?

Mary cuts an apple pie into 8 pieces. She cuts half of the pieces into thirds for the children. She cuts 75 percent of the remaining pieces in half for her friends. How many pieces of pie are there in total now?

A teacher scored a student's test of 30 questions by subtracting 2 times the number of incorrect answers from the number of correct answers. If the student answered all of the questions, which of the following could be the score the student received?

I. 15

II. 18

III. 25

A man who died left an estate valued at $111,000. His will stipulated that his estate was to be distributed so that each of his three children received from the estate and his previous gifts, combined, the same total amount. If he had previously given his oldest child $15,000, his middle child $10,000, and his youngest $2,000, how much did the youngest child receive from the estate?

Roy is now 4 years older than Erik and half of that amount older than Iris. If in 2 years, Roy will be twice as old as Erik, then in 2 years what would be Roy’s age multiplied by Iris’s age?

A canoeist spent two days on a large lake. On the second day, the canoeist rowed 2 hours longer and at an average speed 2 miles per hour faster than he rowed on the first day. If the canoeist traveled a total of 50 miles and spent a total of 12 hours rowing on his trip, what was his average speed on the first day?