You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

Question: One-tenth of the students at a nursery school are 4 years old or older. If 20 students have not yet reached their third birthday, and a total of 50 students are not between 3 years old and 4 years old, how many children are in the nursery school?

 Option A: 150

 Option B: 300

 Option C: 450

 Option D: 490

 Option E: 620
Option B

Question: In how many ways can the letters of word DEVELOP be arranged such that all the vowels as well as all the Consonants always appear together?

 Option A: 9!

 Option B: 3!*4!*2!

 Option C: 5!*5!

 Option D: 5!*4!*2!

 Option E: 6!*4!
Option B

Question: Ifaequals the sum of the even integers from 2 to 20, inclusive, andbequals the sum of the odd integers from 1 to 19, inclusive, what is the value of b - a ?

 Option A: -10

 Option B: 10

 Option C: -19

 Option D: 20

 Option E: 21

Option A