I earned my first payout by answering textbooks on environmental science. At first, I was just answering the questions for fun because it was the same textbook we're using in class. For every question, the site pays $1, and they're not quite strict when it comes to the length of your answers provided that you were able to provide what is asked. Back then, I was able to answer 10 questions straight. Though, I kinda worry as the site pays 4 months after the answer was reviewed. I thought I was being fooled because it was too late. But then it was indeed after a month when I received an email saying that the $10 payment was already transferred to my Paypal account.
However, I got so busy with work and studies that I wasn't able to visit the site again. When I checked it last month, they reduced the payment to $0.50 per question. But still, it was a decent amount of money given that one can easily answer 100 questions in one sitting. And the good news is that, the review and payment is made quite faster than before.
I was very glad to come across that site because it did not only gave me an opportunity to earn but also a chance to review my lessons.