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Permutations and Combinations Questions - Permutation and Combinations

11:  

If a five digit number divisible by 3 is to be formed using the numerals 0, 1, 2, 3, 4 and 5, without repetition, then total number of ways this can be done is

A.

216

B.

240

C.

600

D.

3125

 
 

Option: A

Explanation :

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berihun said: (9:26pm on Friday 5th May 2017)
the answer i s " C "!! b/c 1st digit =5 ways 2nd digit=5ways 3rd digit =4 ways 4th=3 ways 5th digit =2 ways b/c repeatition is not allowd answer=5*5*4*3*2=600

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12:  

If sides AB, BC, CA of a triangle ABC have 3, 4 and 5 interior points respectively on them, then total number oftriangles that can be constructed by using these points as vertices, is

A.

220

B.

204

C.

205

D.

195

 
 

Option: C

Explanation :

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13:  

A student can take one of four Mathematics sections and one of five English sections. The number n of ways he can register for the two courses, is

A.

4

B.

5

C.

20

D.

30

 
 

Option: C

Explanation :

There are four choices for Mathematics and five choices for English.
n= 4 x 5= 20

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14:  

There are 10 lamps in a hall. Each one of them can be switched on independently. The number of ways in which the hall can be illuminated is

A.

102

B.

1023

C.

210

D.

10!

 
 

Option: B

Explanation :

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SASIKALA K said: (9:35am on Wednesday 21st February 2018)
Total number of lamps =10Since at least one lamp is to be kept switched onThe total number of ways are10C1 10C2 ....10C1010C1 10C2 ....10C10⇒210−1⇒210−1⇒1024−1⇒1024−1⇒1023

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15:  

The number of ways in which 10 persons can sit around a circular table so that none of them has ~he same neighbours in any two aITangem~nts, is

A.

9!

B.

C.

10!

D.

 
 

Option: B

Explanation :

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