TASK DEFINITION: In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.
PROBLEM: Article: Mark Twain was a famous American writer in his day. He liked to play jokes on his friends. One day one of his friends lost his wallet and asked Mark Twain to pay his train ticket for him. "But I don't have enough money to pay both your ticket and mine," Mark Twain said. The friend didn't know what to do. "We can do this," said Mark Twain." We can get on the train and when the conductor came to check the tickets , you can hide under my seat." Later, however, when the conductor came to check the tickets, Mark Twain gave him two tickets --- one for himself and one for his friend . Then he explained in aloud voice," My friend is a strange man. When he travels on a train, he does not like to sit on the seat." Of course everyone in the train looked at the poor friend under the seat and laughed at him loudly.
Answer: Because the friend lost his money.

SOLUTION: Why did the friend ask Mark Twain to pay his train ticket for him?

PROBLEM: Article: My 11-year-old son and I rides bikes to and from his school every day. I accompany him on the 20-minute ride through Manhattan, drop him off and return at the end of day to pick him up. We always ride together; sometimes he leads; sometimes I do. And as we ride, we communicate the ways to minimize the dangers: Don't go too fast, and watch out for doors suddenly swinging out from parked cars and jaywalking pedestrians, etc. Some friends worry about the risk of riding in traffic, but is there a better way to let my son know how to deal with traffic dangers? But recently he requested me to start hanging back a half block or so. This way he could enjoy the feeling of riding on his own, with the security of knowing that I was nearby in case he needed me. This is healthy, of course, as my son needs space to develop independence in preparation for his inevitable (,) departure from home. However, that means soon he will want to ride to school on his own, and I will no longer have this wonderful routine. "Let your children go if you want to keep them." I understand this and am trying to let my son go in age-appropriate phases, but I still suffer. It's one of the most troubling experiences of parenthood -- recognizing that your presence is becoming less welcome. My dilemma as a husband mirrors the concern I feel as a parent. My wife has just left on a six-month mission to cover the situation in Libya. In the days leading up to her departure, we spoke openly about the possibility, however unlikely, that she might be killed. But while I influence her decisions, I do not control them. Finally, it was her decision. I know that letting go is the wisest path in this case too. As we travel through life's phases, we must let go of so much. And I don't think it gets easier with practice. But maybe just accepting that eventually we will have to let go is the secret to living a full life.
Answer: To teach his son to ride in traffic.

SOLUTION: Why does the writer accompany his son on his daily ride to school?

PROBLEM: Article: Buffet is the son of the best investor Warren Buffet, and he's the CEO of a philanthropic foundation . But he's also a lifelong farmer. He is familiar with the saying that each farmer can expect to have 40 opportunities to improve their harvest. And it's not just farmers who know there's a clock running on their efforts. " We all need to recognize that we only have a fixed amount of time to affect change," said Howard G. Buffett(HGB) HGB wants to invest more than $3 billion, in an effort to end global hunger and poverty for the world's nearly one billion poor people by 2045. He's decided to focus much of his effort on farming in the developing world. He believes that the best way to deal with poverty is to change the lives of farmers in the poorest nations on the planet. "It's a pretty well proven fact that nothing works better at bringing people out of poverty than investment in rural areas," said HGB. Healthy soils are a most important part of productive farmers, but 1.5 billion people -- a fifth of the global population -- live on poor land. "You have to fix the soil," he said. HGB also has the idea that farmers who own their own land will raise crops with an eye to the long-term health of the soil. He would like to see that balanced with a foreign-aid plan. HGB notes that too often, experts want to make agriculture in developing nations look like farming in rich countries." It's not going to happen like that," said HGB. "You need to consider local differences, local culture." Many more ideas of HGB can be found in his new book, Forty Chances: Finding Hope in a Hungry World.
Answer: 7.5 billion

SOLUTION:
What's the population of the whole world?