Challenge quiz – Three questions from Number Theory

Hi all,

I have given below three questions from Number Theory from the quiz that is on our website (We have already discussed three out of these). I will post the solutions for this in a day or two.

Happy cracking.

1. What is the smallest number that has exactly 12 factors?

a. 211
b. 60
c. 120
d. 96
e. 144

2. If f(x) is the number of primes less than or equal to x, find the value of f(90) – f(80) = ?
a. 3
b. 2
c. 1
d. 4
e. 0

3. The difference between the ages of two brothers is a prime number. Sum of their ages is also a prime number. If the elder brother is 28 years old, how many different values can the age of the younger brother take?

a. 2
b. 3
c. 4
d. 1
e. 0

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