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Aptitude - Numbers

Exercise : Numbers - General Questions
101.
The sum of even numbers between 1 and 31 is:
6
28
240
512
Answer: Option
Explanation:

Let Sn = (2 + 4 + 6 + ... + 30). This is an A.P. in which a = 2, d = 2 and l = 30

Let the number of terms be n. Then,

a + (n - 1)d = 30

     2 + (n - 1) x 2 = 30

    n = 15.

Sn = n (a + l) = 15 x (2 + 30) = (15 x 16) = 240.
2 2

102.
If the number 91876 * 2 is completely divisible by 8, then the smallest whole number in place of * will be:
1
2
3
4
None of these
Answer: Option
Explanation:

Then number 6x2 must be divisible by 8.

   x = 3, as 632 is divisible 8.

103.
2056 x 987 = ?
1936372
2029272
1896172
1926172
None of these
Answer: Option
Explanation:
2056 x 987 = 2056 x (1000 - 13)
= 2056 x 1000 - 2056 x 13
= 2056000 - 26728
= 2029272.
104.
On multiplying a number by 7, the product is a number each of whose digits is 3. The smallest such number is:
47619
47719
48619
47649
Answer: Option
Explanation:

By hit and trial, we find that

47619 x 7 = 333333.

105.
If 60% of 3 of a number is 36, then the number is:
5
80
100
75
90
Answer: Option
Explanation:

Let the number be x. Then

60% of 3 of x = 36
5

60 x 3 x x = 36
100 5

x = 36 x 25 = 100
9

Required number = 100

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