Mark the correct alternative in the following:

The 10th common term between the A.P.s 3, 7, 11, 15, ... and 1, 6, 11, 16, ... is


Here, common difference of first A.P. is d=7-3=4


And common difference of second A.P. is d’=6-1=5


Now L.C.M of d and d’=(4,5)=20


Also first common term in both A.P.s is 11.


We have to find 10th common term i.e. n=10


Consider an A.P. in which a=11,d=20 and n=10


Then, a10=a+(10-1)d


=11+9×20


=11+180


=191

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