A satellite is composed of 24 modular units, each of which is equipped with a set of sensors, some of which have been upgraded. Each unit contains the same number of non-upgraded sensors. If the number of non-upgraded sensors on one unit is 1/3 the total number of upgraded sensors on the entire satellite, what fraction of the sensors on the satellite have been upgraded? Select:
A) 5 / 6 B) 1 / 5 C) 1 / 6 D) 1 / 9 E) 1 / 24

Rationale: let x be the number of upgraded sensors on the satellite . the number of non - upgraded sensors per unit is x / 3 . the number of non - upgraded sensors on the whole satellite is 24 ( x / 3 ) = 8 x . the fraction of sensors which have been upgraded is x / ( x + 8 x ) = x / 9 x = 1 / 9 the answer is d .
Answer: D