Number System-Railway Maths Part VI

Total Questions: 50

21. Find the ninth term of an arithmetic progression with the first term as 5 and the common difference as 4. [RRB NTPC 08/02/2021 (Evening)]

Correct Answer: (c) 37
Solution:

1st term (a)
= 5, common difference (d) = 4
9th term of AP = a + (n - 1)d
= 5+ (9 - 1)4 ⇒ 5 + 32 = 37

22. Consider the following statements and decide which of them are correct. [RRB NTPC 09/02/2021 (Morning)]

(1) Every prime number is odd.

(2) Product of any two prime numbers is odd

Correct Answer: (c) Neither 1 nor 2
Solution:

Both statements incorrect. are

23. An Army General wishes to arrange his 40125 soldiers in rows and columns in the form of a square. After arranging them, he found that some of them are left out. How many soldiers are left out ? [RRB NTPC 09/02/2021 (Morning)]

Correct Answer: (b) 125
Solution:

Nearest square of 40125 is 40000 = (200)²
Soldier left = 40125 - 40000 = 125

24. Which of the following statement(s) is/are true. [RRB NTPC 09/02/2021 (Morning)]

(1) Every whole number is a natural number.

(2) Every integer is a rational number.

(3) Every rational number is an integer.

Correct Answer: (b) 2
Solution:

Every integer is a rational number.

25. In a five digit number, the digit in the hundred's place is 2 and the digit in the unit's place is twice the digit in the hundred's place. The number has no thousands. The digit in the ten thousand's place is the sum of the digit in the hundred's place and the digit in the unit's place. The digit in the ten's place is the digit in the ten thousand's place minus 1. The number is: [RRB NTPC 09/02/2021 (Morning)]

Correct Answer: (a) 60254
Solution:

Hundreds place = 2
Unit place = 2 × 2 = 4
Thousand place = 0
Ten thousand place = 6, Ten place = 5
So that, Number = 60254

26. The least number by which 294 must be multiplied to make it a perfect square is: [RRB NTPC 09/02/2021 (Morning)]

Correct Answer: (d) 6
Solution:

When 294 is multiplied with 6 then we have a perfect square.
294 × 6 = 1764 , √1764 = 42

27. What is the value of the digits A and B? [RRB NTPC 09/02/2021 (Morning)]

BA × B3 = 57A

 

Correct Answer: (a) A = 5 B = 2
Solution:

BA × B3 = 57A
By the option
Only A = 5 , B = 2 is satisfied by the given equation.

28. What is the unit digit in the following product? [RRB NTPC 09/02/2021 (Evening)]

91 × 92 × 93 × ...........× 99

Correct Answer: (c) 0
Solution:

91 × 92 × 93 × ...........×99
When 2 of 92 and 5 of 95 are multiplied it will make 10.
Now any number multiplied with 10, its unit digit will be 0.

29. If the numbers divisible by 3, from 1 to 30, are arranged in descending order, which number will be at the 7th place from the bottom? [RRB NTPC 09/02/2021 (Evening)]

Correct Answer: (d) 21
Solution:

Number which are divisible by 3, from 1 - 30
3, 6, 9, 12, 15, 18, 21, 24, 27 ,30
Now in descending order 30, 27, 24, 21, 18, 15, 12, 9, 6, 3
7th from the bottom = 4th from the top Number = 21

30. What is the sum of the squares of the numbers from 3 to 18? [RRB NTPC 09/02/2021 (Evening)]

Correct Answer: (b) 2104
Solution:

Sum of squares from 1 to 18
= (18×(18 + 1)(2 × 18 + 1))/6
= (18 × 19 × 37)/6 = 2109
Sum of squares from 3 to 18
= 2109 - 1 - 4 = 2104