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
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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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