Aptitude - Numbers

Exercise : Numbers - General Questions
56.
9 + 3 + 7 + 2 - 9 + 1 = ?
4 17 15
7 + 719
1020
9 + 817
1020
9 + 719
1020
7 + 817
1020
None of these
Answer: Option
Explanation:
Given sum
= 9 + 3 + 7 + 2 - 9 + 1
4 17 15
= (9 + 7 - 9) + 3 + 2 - 1
4 17 15
= 7 + 765 + 120 - 68
1020
= 7 + 817
1020

57.
1 - 1 + 1 - 2 + 1 - 3 + ... up to n terms = ?
n n n
1 n
2
1 (n - 1)
2
1 n(n - 1)
2
None of these
Answer: Option
Explanation:
Given sum
= (1 + 1 + 1 + ... to n terms) - 1 + 2 + 3 + ... to n terms
n n n
= n - n 1 + 1     [ Ref: nth terms = (n/n) = 1]
2 n
= n - n + 1
2
= 1 (n - 1)
2

58.
On dividing 2272 as well as 875 by 3-digit number N, we get the same remainder. The sum of the digits of N is:
10
11
12
13
Answer: Option
Explanation:

Clearly, (2272 - 875) = 1397, is exactly divisible by N.

Now, 1397 = 11 x 127

The required 3-digit number is 127, the sum of whose digits is 10.


59.
A boy multiplied 987 by a certain number and obtained 559981 as his answer. If in the answer both 9 are wrong and the other digits are correct, then the correct answer would be:
553681
555181
555681
556581
Answer: Option
Explanation:

987 = 3 x 7 x 47

So, the required number must be divisible by each one of 3, 7, 47

553681 (Sum of digits = 28, not divisible by 3)

555181 (Sum of digits = 25, not divisible by 3)

555681 is divisible by 3, 7, 47.


60.
How many prime numbers are less than 50 ?
16
15
14
18
Answer: Option
Explanation:

Prime numbers less than 50 are:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47

Their number is 15