[1/(1.2.3)] + [1/(2.3.4)] + [1/(3.4.5)] + [1/(4.5.6)] is equal to
Select:
A) 7 / 30
B) 11 / 30
C) 13 / 30
D) 17 / 30
E) none

Rationale: answer given exp . = [ ( 4 x 5 x 6 ) + ( 5 x 6 ) + ( 2 x 6 ) + ( 2 x 3 ) ] / [ ( 2 x 3 x 4 x 5 x 6 ) ] = 168 / ( 24 x 30 ) = 7 / 30 correct option : a
Answer: A