Question

1. The nth terms of the two series 3 + 10 + 17 + .... and 63 + 65 + 67 + .... are equal, then the value of ‘n’
is [ ]
a) 9 b) 13 c) 19 d) 11

Answer 1

Answer:

LET A.P 1 BE 3,10,17 .............n  &   let AP2 be 63,65.............n

a=3;d=7                                       &   A=63 ; D=2  

an=a+(n-1)d                                 & An=A+(n-1)D

an=3+(n-1)7                                 & An=63+(n-1)2

an=3+7n-7                                   & An=63+2n-2

an=7n-4                                       & An=61+2n

As an=An

∴7n-4=61+2n

∴7n-2n=61+4

∴5n=65

∴n=65/5

∴n=13.

hence option b is correct .

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