If n is a positive integer and r is the remainder when (n - 1)(n + 1) is divided by 24, what is the value of r ?

(1) n is not divisible by 2.
(2) n is not divisible by 3.

Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it. If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1) The probability that the ball will both be white and have an even number painted on it is 0.
(2) The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2.

If n is a positive integer and r is the remainder when 4 + 7n is divided by 3, what is the value of r ?

(1) n + 1 is divisible by 3.
(2) n > 20

A store sells milk in cartons of two sizes, one-half gallon and one-quarter gallon. If the store sold a total of 300 cartons of milk yesterday, how many gallons of milk did it sell yesterday?

(1) Yesterday the store sold 120 one-quarter-gallon cartons of milk.
(2) Yesterday the store sold 90 gallons of milk in one-half-gallon cartons.

Did it take Pei more than 2 hours to walk a distance of 10 miles along a certain trail? (1 mile = 1.6 kilometers, rounded to the nearest tenth.)

(1) Pei walked this distance at an average rate of less than 6.4 kilometers per hour.
(2) On average, it took Pei more than 9 minutes per kilometer to walk this distance.

The sum of positive integers x and y is 77. What is the value of xy ?

(1) x = y + 1
(2) x and y have the same tens digit.

If xyz > 0, is x > 0 ?

(1) xy > 0
(2) xz > 0

If m, r, x, and y are positive, is the ratio of m to r equal to the ratio of x to y ?

(1) The ratio of m to y is equal to the ratio of x to r.
(2) The ratio of m + x to r + y is equal to the ratio of x to y.

In the xy-plane, does the line with equation y = 3x + 2 contain the point (r, s) ?

(1) (3r + 2 - s)(4r + 9 - s) = 0
(2) (4r - 6 - s)(3r + 2 - s) = 0

Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force are directors?

(1) The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all employees on the task force.
(2) The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all employees on the task force.