C and E can be easily eliminated
Now we have to choose between A, B or D
"Charging a flat rate of $20 per month and $0.50 for every minute over 200 minutes" means
0 to 200 mins- $20 fixed
from 201st min on wards- $1/2 for every min
B. Two-thirds of the company's customers use less than 500 minutes per month
Let there be 3K customers
Under New plan(N):
All will be charged=(3K) X 50= 150K
Under Old plan(O):
(I)2/3=2K customers ( say they use an avg of 400 min)
fixed :2K X 20= 40K
variable:(400-200)X1/2X2K=200K( here itself the revenue has increased over old plan i.e, 240K when we have calculated for 2/3rd alone. When we add revenue from remaining 1/3, total revenue will be even more higher.
(II)1/3=1K
fixed :
variable:
i.e,{ total of old plan (I)+(II)}>new plan which suggests that the new plan will actually NOT increase the company's revenue.
D) One-fifth of the company's customers use in excess of 1,000 minutes per month.
Under New plan(N):
3K X 50= 150 K
Under Old plan(O):
(I)1/5= 600 customers ( say they talk for avg of 1100min)
fixed :600X50=30K
variable:(1100-200)X1/2X600=270K
HERE ALSO the revenue has increased over old plan i.e, 300K when we have calculated for 2/3rd alone. When we add revenue from remaining 4/5, total revenue will be even more higher.
(II)4/5= 2400 customers
fixed :
variable:
i.e,{ total of old plan (I)+(II)}>new plan which suggests that the new plan will actually not increase the company's revenue.
both B and D are satisfying the condition.
Bumping for further review and discussions.