Question: A train 110 meters long completely crosses a 280 meters long bridge in 38 seconds. What is the speed of the train is?
Options:
(A) 32
(B) 45
(C) 40
(D) 66
(E) 09
Answer: S = (110 + 280 /38 = 390/38 * 18/5 = 40
The answer is (C).

Question: There are 10 female and 15 male in a work place. In how many ways can a person can be selected?
Options:
(A) 20
(B) 15
(C) 18
(D) 40
(E) 25
Answer: No of ways = 10+ 15 = 25
The answer is (E).

Question: What is the least number should be added to 1056, so the sum of the number is completely divisible by 25?
Options:
(A) 19
(B) 20
(C) 32
(D) 41
(E) 53
Answer: (1056 / 25) gives remainder 6
19 + 6 = 23, So we need to add 19
The answer is (A).

Question: If X is the sum of first 20 positive even integers and Y is the sum of first 20 positive odd integers, what is the value of x-y?
Please try to explain your answers
Options:
(A) 0
(B) 20
(C) 50
(D) 75
(E) 100
Answer:

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
First even minus first odd = 2-1 = 1;
The sum of first 2 even integers minus the sum of first 2 odd integers = (2+4)-(1+3) = 2;
The sum of first 3 even integers minus the sum of first 3 odd integers = (2+4+6)-(1+3+5) = 3;
We can see the patterns here, so the sum of first 20 positive even integers minus the sum of first 20 positive odd integers will be 20.
The answer is (B).