One more coin

28/04/11 10:24
There are 101 completely unbiased identical coins. You give your friend 50 and you take 51 of them. Both of you toss all the coins you have. What is the probability that you will land up with more heads than your friend?

(posted on Facebook on 4/27/2011)

Table and coins

21/04/11 10:01
You and your friend are sitting across a perfectly round table and have a bunch of identical quarters. You two will alternately place quarters flat on the table such that a quarter will not overhang the boundary of the table nor overlap on another quarter. Whoever runs out of space, loses. You go first. How will you ensure that you win?

(posted on Facebook on 4/21/2011)

Braking a 40 lb rock

14/04/11 10:07
You have a stone weighing 40 pounds. You have to break it up into 4 parts such that using those weights in a scale and pan balance you can weigh anything from 1 pound to 40 pounds (integers only) Example: if you broke them as 5,5, 7 and 23, you can get 2 by putting 7 on one side and 2 on another. What are those 4 weights?

(posted on Facebook on 4/14/2011)

7 with three 2s

09/04/11 08:56
How can you get 7 using only three 2s. You can use plus, minus, multiply, divide, square root, factorial, decimal point, log, "to the power of" and parentheses. As many times as you want. You can also put digits together to form ... let's say 22.

(posted on Facebook on 4/9/2011)

64 with 2 4s

31/03/11 10:09
Using only two 4's how would you get 64? You can use standard mathematical functions found on a calculator - plus, minus, multiply, divide, to the power, log, square root, factorial.... Cannot use trigonometry or any other digit.

(posted on Facebook on 3/31/2011)