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The number of common terms in the two sequences 17, 21, 25,…..417 and 16, 21 26,.....466 is

  1. 78
  2. 19
  3. 20
  4. 27
  5. 22
asked in Quantitative Aptitude by (7.6k points)  
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2 Answers

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Alternate method :

difference of first series = 4, difference of second series =5 

so difference of common series will be always  LCM (4,5 )= 20 .

by seeing both series ...we can easly find first term = 21,

and last term of common series will be less than or equal to 417 ,bcoz common series will go up to common of both and first sequence is till 417 .

series like 21 ,41,61.... 401....(bcoz 401%20=1 ,) 

so 401= 21+ (n-1)20 

      380/20= (n-1)

    n= 20 hence answe is 3)

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No of terms in first sequence be n

417=17+(n-1)4

n=101

No of terms in second seq be m

466=16+(m-1)5

m=91

First common term is 21 next is 41

Common difference=20

Now last common term will be less than or equal to 417 and not 466

Last term in common seq will be 401

401=21+(k-1)20

380/20=k-1

k=20
answered by (1.6k points)  

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