Numbers - General Questions (10)

73.

(800 ÷ 64) x (1296 ÷ 36) = ?

A.	420
B.	460
C.	500
D.	540
E.	None of these

Answer: Option E

Explanation:

Given Exp. =	800	x	1296	= 450
	64		36

74.

(51 + 52 + 53 + ... + 100) = ?

A.	2525
B.	2975
C.	3225
D.	3775

Answer: Option D

Explanation:

S_n = (1 + 2 + 3 + ... + 50 + 51 + 52 + ... + 100) - (1 + 2 + 3 + ... + 50)

=	100	x (1 + 100) -	50	x (1 + 50)
	2		2

= (50 x 101) - (25 x 51)

= (5050 - 1275)

= 3775.

75.

When a number is divided by 13, the remainder is 11. When the same number is divided by 17, then remainder is 9. What is the number ?

A.	339
B.	349
C.	369
D.	Data inadequate

Answer: Option B

Explanation:

x = 13p + 11 and x = 17q + 9

13p + 11 = 17q + 9

17q - 13p = 2

q =	2 + 13p
	17

The least value of p for which q =	2 + 13p	is a whole number is p = 26
	17

x = (13 x 26 + 11)

= (338 + 11)

= 349

76.

How many prime numbers are less than 50 ?

A.	16
B.	15
C.	14
D.	18

Answer: Option B

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

77.

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:

A.	553681
B.	555181
C.	555681
D.	556581

Answer: Option C

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.

78.

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:

A.	10
B.	11
C.	12
D.	13

Answer: Option A

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.

79.

	1 -	1		+		1 -	2		+		1 -	3		+ ... up to n terms = ?
		n					n					n

A.	1/2 n
B.	1/2 (n - 1)
C.	1/2 n(n - 1)
D.	None of these

Answer: Option B

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

80.

9 +	3	+ 7 +	2	-		9 +	1		= ?
	4		17				15

A.	7 + 719/1020
B.	9 + 817/1020
C.	9 + 719/1020
D.	7 + 817/1020
E.	None of these

Answer: Option D

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

Numbers - General Questions (10)

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