A caterer normally charges $15 per person plus a $10 delivery fee

Official solution from Veritas Prep.

The question asks you "by what percent is her total cost greater." Therefore, you must be able to calculate both the total for ordering in advance and the total for ordering same day.

Statement 1 tells you the delivery fee for same-day orders -- $20. This is 200% of the original $10 delivery fee.

Since we know the per-person charge for the advance orders and same-day orders, you might be tempted to believe that is sufficient. HOWEVER, we cannot calculate the total without knowing exactly how many people there are. (One could easily assume that there is just one person -- Amy -- but before jumping to that conclusion note that Amy orders "for her company," and take a minute to look at Statement 2.) Statement 1 alone is not sufficient.

Statement 2 provides information regarding the total number of people, but we do not know the rush delivery fee. Therefore, Statement 2 alone is not sufficient.

Together, Statement 1 and Statement 2 provide sufficient information to calculate the new total charge. Putting together the rush delivery fee and the number of people, combined with the original numbers provided, we can calculate the original charge, the new charge, and therefore the percentage increase.