PS Question

For any positive integer n, the sum of the first n positive integers equals n(n+1)/2. What is the sum of all even integers between 99 and 301? a. 10,100 b. 20,200 c. 22,650 d. 40,200 e. 45,150 Why is it 2(150(150+1))/2 - 2(49(49+1))/2, instead of 150(150+2)/2 - 49(49+1)/2??? Why do I have to multipl...

OG12 PS #148

What is the quickest way to solve this?

If x, y, and k are positive numbers such that (x/x+y)(10) + (y/x+y)(20)= k and if x is less than y, which of the following could be the value of k?

a. 10
b. 12
c. 15
d. 18
e. 30

The MGMAT explanation says use:

(7*6)/2 to come to 21 combinations

Where do the 7 and 6 come from?

MGMAT CAT PS Question 700+

In a room filled with 7 people, 4 people have exactly 1 sibling in the room and 3 people have exactly 2 siblings in the room. If two individuals are selected from the room at random, what is the probability that those two individuals are NOT siblings? a. 5/21 b. 3/7 c. 4/7 d. 5/7 e. 16/21 I don't fu...

PS OG91

Store sells all maps at one price and all books at another price. Monday the store sol 12 maps and 10 books totally $38. Tuesday the store sold 20 maps and 15 books for $60. How much less does a map sell for than a book? a $.25 b $.50 c $.75 d $1.00 e $1.25 I realize that the two equations are 12m+1...

OG PS65

Another question for you guys. I need a clear explanation for this one. I don't follow the OG's steps. A certain fruit stand sells apples for $0.70 each and bananas for $0.50 each. If a customer purchased both apples and bananas from the stanf for a total of $6.30, what total number of apples and ba...

OG PS28

I am not totally understanding the OG explanation to arrive at this solution. The average distance between the Un and a certain planet is approximately 2.3*10^14 inches. Which of the following is closest to the average distance between the Sun and the planet, in kilometers? (1 kilometer is approxima...