Math Riddles

Answer: No. When you remove the two diagonal spaces from the chess board they are both black or both white, making it so that there are two more of the other color. Each domino would cover 1 black and 1 white space. So 31 of them would have to cover 31 white spaces and 31 black spaces but with the corners removed there are 30 of one color and 32 of the other.

Answer: 90 percent. If you pick the heads coin the chance of getting the first 2 heads is 100 percent (4/4) and if you pick the fair coin the chance is 25 percent (1/4). So from this, the chance that it is the heads coin is 4/5 and the fair coin 1/5.

Then, if it is the heads coin you will definitely get heads (4/5). If you flip the fair coin it is 1/10 (1/5 * 1/2). Add the probabilities together: 4/5 + 1/10 = 9/10.

Answer: Just 2.

Each time you give the owner of a bridge half of your brownies (1 brownie) they give you one back as well.

Answer: 7. If you break the batteries into 3 groups: Two groups of 3 and one group of 2. By doing this you guarantee that one of the groups has 2 working batteries. Both of the groups of 3 have 3 possible combinations of 2 batteries and the group of 2 only has 1 combination. So, 3 + 3 + 1 = 7 tries at most to find two working batteries.

Answer: Cut a small hole in a piece of paper that is just large enough to see Waldo. This way you don't reveal anything about where he is, just that he is there.