3r ≤ 4s+5
|s|≤5 

Given the inequalities above, which of the following CANNOT be the value of r ?

　AB
＋BA
  AAC

In the correctly worked addition problem shown, where the sum of the two-digit positive integers AB and BA is the three- digit integer AAC, and A, B, and C are different digits, what is the units digit of the integer AAC ?

For a light that has an intensity of 60 candles at its source, the intensity in candles, S, of the light at a point d feet from the source is given by the formula

s=~$60k \over d^2$~ where k is a constant. If the intensity of the light is 30 candles at a distance of 2 feet from the source, what is the intensity of the light at a distance of 20 feet from the source?

(~$1 \over 5$~)² -(~$1 \over 5$~)(~$1 \over 4$~ ) =

One inlet pipe fills an empty tank in 5 hours. A second inlet pipe fills the same tank in 3 hours. If both pipes are used together, how long will it take to fill ~$2 \over 3$~ of the tank?

Which of the following lines in the xy-plane does not contain any point with integers as both coordinates?

If x = -|w|, which of the following must be true?

A garden center sells a certain grass seed in 5-pound bags at $13.85 per bag, 10-pound bags at $20.43 per bag, and 25-pound bags at $32.25 per bag. If a customer is to buy at least 65 pounds of the grass seed, but no more than 80 pounds, what is the least possible cost of the grass seed that the customer will buy?

The average (arithmetic mean) length per film for a group of 21 films is t minutes. If a film that runs for 66 minutes is removed from the group and replaced by one that runs for 52 minutes, what is the average length per film, in minutes, for the new group of films, in terms of t ?

If x and y are integers such that 2 < x ≤ 8 and 2 < y ≤ 9, what is the maximum value of ~$1 \over x$~ - ~$x \over y$~ ?