**Number System – Tnpsc Aptitude Pdf Download Questions With Answers in Tamil & English**

Tnpsc Aspirants can get Number System – Tnpsc Aptitude Pdf Download Questions With Answers in Tamil & English from below Passage. Aptitude & mental ability section contains 25 questions in group 2 and 45 question in group 1 exam. This below study materials helps you to get High marks in Tnpsc maths section.

**Tnpsc Solved Number System Sums**

1. Which of the following is prime numbers?

(a) 149

(b) 43

(c) 319

(d) 197

**Answer:** (a)

**Explanation:**

Test for prime numbers:

For numbers less than 100, it is not very difficult to determine whether it is a prime number or not. We can also check it up from the given under prime numbers.

For testing any number greater than 100 whether it is a prime number or not:

Step 1: |
We take the nearest integer larger than the approximate square root of that number. Suppose it is X. |

Step 2: |
We test the divisibility of the given number by every prime number less than X. |

Step 3: |
If the number is not divisible by any of them, then it is prime number. Otherwise it will be considered as a composite number. |

We know that

Prime numbers less than 14 are 2, 3, 5, 7, 11, and 13

Clearly none of the number divides 149

Therefore, 149 is a prime number.

2. Which of the following is not prime number?

(a) 149

(b) 137

(c) 319

(d) 811

**Answer:** (c)

**Explanation:**

We know that

Prime numbers less than 18 are2, 3, 5, 7, 11, 13 and 17

Out of these prime numbers, 11 divide 319 completely.

3. A prime number N, in the range 10 to 50, remains unchanged when its digits are reversed. The square of such a number is: [CDS 2002]

(a) 1936

(b) 1089

(c) 484

(d) 121

**Answer:** (d)

**Explanation:**

Numbers from 10 to 50, which are remains same when digits are reversed is 11, 22, 33 and 44.

Here, except 11 all are not a prime numbers.

The required prime number is 11, so its square is 121.

4. For what value of n are prime numbers? [CDS 2006]

(a) 3

(b) 5

(c) 2

(d) 1

**Answer:** (c)

**Explanation:**

As per the condition, 2 is the answer.

5. What are the prime factors of 70?

(a) (2, 3, 5)

(b) (3, 5, 7)

(c) (2, 5, 7)

(d) (11, 7, 2)

**Answer:** (c)

**Explanation:**

Prime factors are 2, 5 and 7

6. The prime factors of 15015 are: [CDS 1997]

(a) 3, 5, 7, 11, 37

(b) 3, 5, 11, 13, 37

(c) 3, 5, 7, 13, 37

(d) 3, 5, 7, 11, 13

**Answer:** (d)

**Explanation:**

Prime factors of 15015 are 3, 5, 7, 11 and 13.

7. The numbers of prime factors in the following expression,

(a) 54

(b) 64

(c) 71

(d) 31

**Answer:** (b)

**Explanation:**

2, 3, 7, 11 are the prime numbers.

The number of prime factors in the given expression = (10+10+17+27) = 64

n=64

8. Three numbers which are co-prime to one another are such that the product of the first two is 77 and last two is143. The sum of the three numbers is: [SSC Grad. 2003]

(a) 15

(b) 27

(c) 31

(d) 39

**Answer:** (c)

**Explanation:**

77 = 11×7

143 = 11×13

7+11+13 = 31

9. The sum of the digits of a two digit number is of the difference between the number and the number obtained by interchanging the position of the digits. What is definitely the difference between the digits of the number? [Bank 2009]

(a) 5

(b) 9

(c) 7

(d) data inadequate

**Answer:** (a)

**Explanation:**

Let the number be 10x +y.

4x = 14y, 2x = 7y

2 and 7 are prime, therefore only x=7 and y=2 satisfy the above condition.

Difference = 7-2=5.

10. There are four prime numbers written is ascending order. The product of the first three is 385 and that of the last three is 1001. Find the first number.

(a) 5

(b) 7

(c) 11

(d) 17

**Answer:** (a)

**Explanation:**

Let the numbers be a, b, c and d

abc=385, bcd=1001

a=5, d=13