Math Riddles

I am an odd number. Take away a letter and I become even. What number am I?

I am a number I am not an odd number I am higher than 90 I am not higher than 100 If you subtract me from 100, you get nothing. What number am I?

In case you were starting to feel confident, this one was meant for third graders in Vietnam. The answer is 66, but we don't blame you for scratching your head about how they got there.

Our product and our sum always give the same answer. Who are we?

How do you go from 98 to 720 using just one letter?

Use the numbers 2, 3, 4 and 5 and the symbols + and = to make a true equation. Conditions: Each must be used exactly once and no other numbers or symbols can be used.

What is the value of 1/2 of 2/3 of 3/4 of 4/5 of 5/6 of 6/7 of 7/8 of 8/9 of 9/10 of 1000?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211