Aptitude - Number System

MCQ

Q 41.

The sum of 5 consecutive even numbers is 70. What is the product of the first and the last number?

Explanation

Let the 5 consecutive even numbers be x, x+2, x+4, x+6 and x+8.

Given, x + (x+2) + (x+4) + (x+6) + (x+8) = 70

Or, x = 10

So, first number = x = 10

And the last number = x+8 = 18

Product = 10x18 = 180

Q 42.

Find the unit digit in (987)⁷⁵⁴

Explanation

(987)⁷⁵⁴

Consider only the unit digit

= (7)⁷⁵⁴

= (7⁴)¹⁸⁸ x (7)²

= (2401)¹⁸⁸ x 49

= (1)¹⁸⁸ x 9

= 9

Q 43.

Find the unit digit in the product of 123x456x789.

Explanation

123x456x789

= 3x6x9 (taking only the unit digit)

= 162

= 2 (Unit digit)

Q 44.

On Salman's birthday Aamir gifted a golden box that was locked with a secret password. Salman can only open the box if he enters the correct password. Aamir loves to play with numbers so he locked the box with a natural number and wrote a riddle on a piece of paper and gifted it along with the golden box. Salman being busy that day asked you to solve the riddle and unlock the box for him.

Riddle: If 1/4 of a number is subtracted from the number itself, it will give a value which is equal to the sum of all the angles of the Bermuda Triangle.

Explanation

Sum of all the angles of a triangle = 180

Let the required number be P.

As per the riddle, P - 1/4P = 180

Or, P = 240

Q 45.

Sum of first 10 natural numbers is?

Explanation

n = 10

Sum = n(n+1)/2 = 55

Q 46.

What is the product of 3rd natural, 2nd prime, 1st whole number?

9
6
0
Infinite

Explanation

3rd natural number = 3

2nd prime number = 3

1st whole number = 0

Product = 3x3x0 = 0

Q 47.

What is the sum of 1st and 2nd prime numbers?

Explanation

1st prime number = 2

2nd prime number = 3

Sum = 2+3 = 5

Q 48.

Find the sum of place and face value of 6 in 654321?

600006
600000
66
12

Explanation

Place value of 6 = 6x100000 = 600000

Face value of 6 = 6

Sum of Place and Face value = 600000 + 6 = 600006

Q 49.

Find the sum of face value of 6 and 9 in 9876?

Explanation

6+9=15

Q 50.

What is the place value of 9 in 9876543210?

9x10⁹
9x10⁶
9x10³
9

Explanation

Place value of 9 = 9x1000000000 = 9x10⁹

Q 51.

What is the place value of 1 in 123?

1
10
100
1000

Explanation

1 is at the hundredth place so, it's place value is 1x100 = 100.

Q 52.

What is the face value of 1 in 123?

1
10
100
1000

Explanation

Face value is equal to the digit itself.