Minnie is making a playlist of songs for a party she will be throwing. She wants the playlist to be an hour long. She has added 16 three-minute songs to the playlist. How many four-minute songs does she have to add to make sure the playlist is an hour long? Give the rationale and then the answer.
Let's think step by step. An hour is equal to 60 minutes. Minnie has 16 * 3 = 48 minutes of songs already on the playlist. She has to fill 60 - 48 = 12 more minutes. Thus, she needs to add 12 / 4 = 3 four - minute songs.. The answer is: 3.

A mountain range has 200 active volcanoes. In a particular year, 20% of the volcanoes exploded in the first two months, 40% of the remaining exploded by the half of the year, and at the end of the year, another 50% of the volcanoes that hadn't already erupted also exploded. How many mountains are still intact at the end of the year? Give the rationale and then the answer.
Let's think step by step. By the first two months, 20 / 100 * 200 = 40 mountains had erupted. The total number of mountains remaining after the first round of explosions is 200 - 40 = 160. When 40% of the remaining mountains exploded, the number of mountains that were still intact decreased by 40 / 100 * 160 = 64. The number of mountains that hadn't exploded after the second explosions is 160 - 64 = 96. When 50% of the mountains which were still intact exploded, the number of mountains that hadn't erupted was reduced by 50 / 100 * 96 = 48. At the end of the year, 96 - 48 = 48 mountains remained intact and hadn't exploded.. The answer is: 48.

Audrey was asleep for 10 hours last night and dreamed for 2/5 of the time. How much of the night was she not dreaming? Give the rationale and then the answer.
Let's think step by step. If Audrey was asleep for 10 hours last night and dreamed for 2 / 5 of the time, she dreamed for 2 / 5 * 10 = 4 hours. The total time Audrey slept without dreaming is 10 - 4 = 6 hours.. The answer is: 6.