A farm used two harvesting machines, H and K, to harvest 100 acres of wheat. Harvesting machine H, working alone at its constant rate, harvested 40 acres of wheat in 8 hours. Then harvesting machine K was brought in, and harvesting machines H and K, working together at their respective constant rates, harvested the remaining acres of wheat in 5 hours. Harvesting machine K harvested how many acres of wheat per hour?

A grocer stacked oranges in a pile. The bottom layer was rectangular with 3 rows of 5 oranges each. In the second layer from the bottom, each orange rested on 4 oranges from the bottom layer, and in the third layer, each orange rested on 4 oranges from the second layer. Which of the following is the maximum number of oranges that could have been in the third layer?

Connie paid a sales tax of 8 percent on her purchase. If the sales tax had been only 5 percent, she would have paid $12 less in sales tax on her purchase. What was the total amount that Connie paid for her purchase including sales tax?

A school purchased 2 computers whose prices were $1,000 and $2,000, respectively. The school is to purchase 2 more computers from a list of computers whose prices range from $1,000 to $2,000, inclusive. The greatest possible average (arithmetic mean) price of the 4 computers is how much greater than the least possible average price of the 4 computers?

The lunch menu at a certain restaurant contains 4 different entrees and 5 different side dishes. If a meal consists of 1 entree and 2 different side dishes, how many different meal combinations could be chosen from this menu?

If x is an even integer and y is an odd integer, which of the following is even?

If ~$\left ( 400 \right )\left ( 6000 \right )=\left ( 240 \right )\left ( 100^{x} \right )$~,what is the value of x ?

A television network sells advertising time on a certain program at the rate of $10,000 per minute. If the program is shown once a day for 5 days a week, what is the cost of advertising on this program for 3 weeks at 30 seconds per day?

In May, Xiang sold 15 used cars. For these 15 cars, the range of the selling prices was $15,000 and the lowest selling price was $4,500. In June, Xiang sold 10 used cars. For these 10 cars, the range of the selling prices was $16,500 and the lowest selling price was $6,100. What was the range of the selling prices of the 25 used cars sold by Xiang in May and June?

9.4 9.9 9.9 9.9 10.0 10.2 10.2 10.5

The mean and the standard deviation of the 8 numbers shown are 10.0 and 0.3, respectively. What percent of the 8 numbers are within 1 standard deviation of the mean?