Good Riddles

Question: If you have an 11 minute and 13 minute hourglass, how can you accurately time 15 minutes?

Question: Use the numbers 2, 3, 4 and 5 and the symbols + and = to make a true equation.

Note: Each must be used exactly once and no other numbers or symbols can be used.

Question: You are my brother, but I am not your brother. Who am I?

Question: 7 months have 31 days. How many months have 28 days?

Question: I have all of your knowledge but could fit in your hands.

What am I?