Questions on permutations?

1. How many arrangements of answers are possible in a multiple-choice test with 10 questions, if each question has four possible answers and only one answer is marked for each question? 2. A school needs to select 2 prefects, one boy and one girl, to attend a leadership camp. If 10 boys and 8 girls apply for the two places, how many possible selections can be made if one of the selected prefects acts as the leader? 3. 20 students are vying for the 3 prizes offered in a Science quiz. How many possible ways are there of awarding the prizes to the top 3 winners? The answer for question 1 from the textbook is 1048576 which is totally not close to my answer through my own solution. I'm not sure if the textbook or my answer is wrong, so can someone check? The answer for question 2 is 80 and question 3 is 6840.