Task: Question Answering
Input (English): Problem: each light bulb at a hotel is either incandescent or fluorescent. at a certain moment, thirty percent of the incandescent bulbs are switched on, and eighty percent of the fluorescent bulbs are switched on. if 40 percent of all the bulbs are switched on at this moment, what percent of the bulbs that are switched on are incandescent ?
Options: a. 20 %, b. 40 %, c. 50 %, d. 60 %, e. 80 %
Output (English): d