During a particular baseball game, the probability of a team's pitcher throwing a strike on each throw is 2/5. What is the least number of times that the pitcher should pitch the ball that will increase the probability of getting a strike at least once to more than 50%.
Options:
(A) 3
(B) 2
(C) 1
(D) 4
(E) 5

Rule of Subtraction: P(A) = 1 - P(A')
Rule of Multiplication: P(A ∩ B) = P(A) P(B)
The probability that the pitcher throws a strike at least once in 2 guesses is 1- (3/5)^2 = 1 - 9/25 = 16/25 > 50%. So the answer is: (B).

A team of eight entered for a shooting competition. The best marks man scored 82 points. If he had scored 92 points, the average scores for. The team would have been 87. How many points altogether did the team score?
Options:
(A) 686
(B) 672
(C) 652
(D) 642
(E) 721

8 * 87 = 696 – 10 = 686 So the answer is: (A).

A certain car uses 12 gallons of gasoline in traveling 180 miles. In order for the car to travel the same distance using 10 gallons of gasoline, by how many miles per gallon must the car’s gas mileage be increased?
Options:
(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

180/10 = 18. The difference is 18 - 15 = 3. So the answer is: (B).

A marble shop contains 5 blue marbles, 5 red marbles, and 5 green marbles. If 2 marbles are purchased at random from the shop, what is the probability that the 2 marbles will be of the red?
Options:
(A) 5/15
(B) 2/21
(C) 20/15
(D) 5/210
(E) 4/14

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Of the 15 marbles we are wanting red:
Probability of choosing 1st red marble: 5/15
Probability of Choosing 2nd red marble: 4/14
Multiply and you get 20/210 simplified to 2/21 So the answer is: (B).