Add me to myself, multiply by four, divide by eight, and you get back to me. What number am I?

I am a number divisible by 3. When you square me, the sum of my new digits equals me. What number am I?

I am a geometric shape with four sides. My opposite sides are parallel, all four of my sides are equal in length, but none of my interior angles are right angles. What shape am I?

Sam gets 4 pumpkins on Monday and 7 pumpkins on Tuesday, then gives away 4. How many pumpkins are left?

If you take away my first letter, I become a heavy weight. If you take away my first two letters, I become an expression of speed. If you take away my first and last letters, I am a unit of distance. What am I?

A lily pad doubles in size every day. If it completely covers a pond in 30 days, on which day did it cover exactly half of the pond?

I am a two-digit prime number. Reverse my digits, and I am still prime. My tens digit is greater than my units digit, and the sum of my digits is 10. What number am I?