maintenance

[khunia]

Each year, 1/6 of the old machines in a factory are replaced with new machines that will remain in use for five years. Approximately what percent of the old machines still remain after two years?

A) 86% B) 77% C) 73% D) 71% E) 69%

[SuM]

Say, total no of machines = 36
After first year no. of Old machines remains = 36 - (36/6) = 30
After 2nd year no. of Old machines remains = 30 - (30/6) = 25

So after 2 years % of old machines that still remain = (25/36)*100 = 69%

answer: E

[ravin]

Let the machines be 100.
Then NUmber of m/c after 1st year: (5/6) of 100
After 2nd year: (5/6)(5/6) of 100

= (25/36) 100 ~ 69%

[khunia]

Yes, Thanks. It's very simply, but I raveled in statement "... that will remain in use for five years."

[300IS]

5/6 x 5/6 = 25/36 ~ 69%..

but that statement of "will remain in use for 5 years" bothers me.. the question asks what percent still remains.. so.. since its only year 1 and 2... doesnt that mean.. all of the machines still remain even though they are replaced??