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Q:

Which of the following has the most number of divisors?

A) 99 B) 101
C) 176 D) 182
 
Answer & Explanation Answer: C) 176

Explanation:

99 = 1 x 3 x 3 x 11

 

101 = 1 x 101

 

176 = 1 x 2 x 2 x 2 x 2 x 11

 

182 = 1 x 2 x 7 x 13

 

So, divisors of 99 are 1, 3, 9, 11, 33, .99

 

Divisors of 101 are 1 and 101

 

Divisors of 176 are 1, 2, 4, 8, 11, 16, 22, 44, 88 and 176

 

Divisors of 182 are 1, 2, 7, 13, 14, 26, 91 and 182.

 

Hence, 176 has the most number of divisors.

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Filed Under: HCF and LCM

Q:

The greatest number which on dividing 1657 and 2037 leaves remainders 6 and 5 respectively, is:

A) 123 B) 127
C) 235 D) 305
 
Answer & Explanation Answer: B) 127

Explanation:

Required number = H.C.F. of (1657 - 6) and (2037 - 5)

= H.C.F. of 1651 and 2032 = 127.

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Filed Under: HCF and LCM

Q:

The least multiple of 7, which leaves a remainder of 4, when divided by 6, 9, 15 and 18 is:

A) 74 B) 94
C) 184 D) 364
 
Answer & Explanation Answer: D) 364

Explanation:

L.C.M. of 6, 9, 15 and 18 is 90.

 

Let required number be 90k + 4, which is multiple of 7.

 

Least value of k for which (90k + 4) is divisible by 7 is k = 4.

 

=>Required number = (90 x 4) + 4   = 364.

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Q:

The product of two numbers is 2028 and their H.C.F. is 13. The number of such pairs is:

A) 1 B) 2
C) 3 D) 4
 
Answer & Explanation Answer: B) 2

Explanation:

Let the numbers 13a and 13b.

Then, 13a x 13b = 2028

=>ab = 12.

Now, the co-primes with product 12 are (1, 12) and (3, 4).

[Note: Two integers a and b are said to be coprime or relatively prime if they have no common positive factor other than 1 or, equivalently, if their greatest common divisor is 1 ]

So, the required numbers are (13 x 1, 13 x 12) and (13 x 3, 13 x 4).

Clearly, there are 2 such pairs.

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Filed Under: HCF and LCM

Q:

Three number are in the ratio of 3 : 4 : 5 and their L.C.M. is 2400. Their H.C.F. is:

A) 40 B) 80
C) 120 D) 200
 
Answer & Explanation Answer: A) 40

Explanation:

Let the numbers be 3x, 4x and 5x.

 

Then, their L.C.M. = 60x.

 

So, 60x = 2400 or x = 40.

 

 The numbers are (3 x 40), (4 x 40) and (5 x 40).

 

Hence, required H.C.F. = 40.

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Q:

Six bells commence tolling together and toll at intervals of 2, 4, 6, 8 10 and 12 seconds respectively. In 30 minutes, how many times do they toll together ?

A) 4 B) 10
C) 15 D) 16
 
Answer & Explanation Answer: D) 16

Explanation:

L.C.M. of 2, 4, 6, 8, 10, 12 is 120.

So, the bells will toll together after every 120 seconds(2 minutes).

In 30 minutes,they will together (30/2)+1=16 times

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Filed Under: HCF and LCM

Q:

The H.C.F. of two numbers is 23 and the other two factors of their L.C.M. are 13 and 14. The larger of the two numbers is:

A) 276 B) 299
C) 322 D) 345
 
Answer & Explanation Answer: C) 322

Explanation:

Clearly, the numbers are (23 x 13) and (23 x 14).

 

 

 

 Larger number = (23 x 14) = 322.

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Q:

Find the ratio in which rice at Rs. 7.20 a kg be mixed with rice at Rs. 5.70 a kg to produce a mixture worth Rs. 6.30 a kg.

A) 1:3 B) 2:3
C) 3:4 D) 4:5
 
Answer & Explanation Answer: B) 2:3

Explanation:

By the rule of alligation:
Cost of 1 kg rice of 1st kind                  Cost of 1 kg rice of 2nd kind 

 

 

  Required ratio = 60 : 90 = 2 : 3

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Filed Under: Alligation or Mixture