A new electric car company holds a limited-time sales event.

The question is a lil unclear, but If I were to go with sumthing, I'd go with [E].

For the car company, the sales for n days of sale would be in the set {3,6,9,.....3n}
Hence total cars sold on n days would be 3n*(n+1)/2

With that in mind, Statement 1, says that if the event had lasted 2 more days, the average number of cars sold per day would have increased by 3. Hence the event lasted for n+2 days.

So Average of cars sold in n+2 days = 3(n+2)*(n+3)/2*(n+2) = (3n + 9)/2
Average of cars sold in n days = 3(n+1)/2 = (3n + 3)/2
Hence the difference is 3, which was calculated for all n. Hence it does not depend on the number of cars sold. Not sufficient.

Statement 2 says, On exactly 9 days during the event, the number of cars for the day is a multiple of 9.
Assuming n = 9, the total number of cars sold = 3*9*10/2 = 15*9 a multiple of 9. Hence the statement is true, but does not specify if n is ultimately 9 or not. It simple states 'On exactly 9 days', and no mention is made if the event ended after the same.

The question is a little confusing. Probably the purpose of it was to do so! Nevertheless, Please verify my answer guerrero25! Hope its correct!

Regards,
Arpan