Official Solution: A language-learning app charges customers on a weekly basis. For billing purposes, a partial week of a subscription is treated as a full week, and the customer is charged the full weekly fee for it. If Laura’s subscription length was converted into billable weeks under this rule, how many billable weeks was she charged for? (1) Laura’s total subscription charge was $180.
This gives the total charge, but it does not give the full weekly fee. So the number of billable weeks cannot be determined.
Not sufficient.
(2) If Laura had ended her subscription 2 days earlier, she would have been charged $45 less.
Since 2 days is less than one week, ending the subscription 2 days earlier could reduce the number of billable weeks by at most 1.
Because the charge would have been $45 less, the reduction must have been exactly 1 billable week, so the full weekly fee was $45.
But we still do not know Laura’s total charge, so we cannot determine how many billable weeks she was charged for.
Not sufficient.
(1)+(2) From statement (2), the full weekly fee was $45.
From statement (1), Laura’s total charge was $180.
So the number of billable weeks was:
\(\frac{180}{45} = 4\)
Sufficient.
Answer: C