[Question]Amanda needs 12 more marbles to have twice as many marbles as Katrina, and Mabel has 5 times as many marbles as Katrina. If Mabel has 85 marbles, how many more marbles does Mabel have than Amanda?
[Answer]Katrina has 85 / 5 = 17 marbles. Twice as many marbles as Katrina is 17 x 2 = 34. Amanda has 34 - 12 = 22 marbles. Mabel has 85 - 22 = 63 more marbles than Amanda. The answer is 63.

[Question]A portable computer drive has enough kilobytes of storage space to store 2000 photos. Each photo is 1.5 kilobytes in size. How many 200-kilobyte videos can it store if it already has 400 photos on it?
[Answer]The drive has 1.5 * 2000 = 3000 kilobytes of storage space. It already has 1.5 * 400 = 600 kilobytes of storage space taken up. Thus, it has 3000 - 600 = 2400 kilobytes of space left. The portable drive can store 2400 / 200 = 12 200 - kilobyte videos on it with 400 photos. The answer is 12.

[Question]Justin bought some jerseys. He bought four long-sleeved ones that cost $15 each, and some striped ones that cost $10 each. How many striped jerseys did Justin buy if he spent a total of $80?
[Answer]Four long - sleeved jerseys cost $15 x 4 = $60. So the striped jerseys amount to $80 - $60 = $20. Hence, Justin bought $20 / $10 = 2 striped jerseys. The answer is 2.

[Question]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?
[Answer]
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.