1. On a test 20 problems were given. Five points were given for each correct answer and 2 points were deducted for each incorrect answer. How many correct answers are required to score 79 on the test?

If you got 16 problems right on the test that would give you an 80 but I don't understand how you would get a 79. Even if you missed one problem, the grade would still be an even number.

2. Write an eight-digit number using the digits 1, 2, 3, and 4 twice each. The 1's should be separated by one digit, the 2's by two digits, the 3's by three digits, and the 4's by four digits.

I don't even know if there is a formula to figure this out. I have just been trying number combinations but have come up with nothing that works so far.

3. Find the numbers that will replace letters a and b so that the five-digit number will be divisible by 36: 19a9b (Note: There are two possible solutions.)

Is there a formula to figure this out or would this be a problem that you would just plug numbers in until it worked? I can plug in the numbers but if there is a formula I would really like to know what it is in case I get another one of these problems.

Thanks for any help!!