为什么是1/4？

刚看到，据说正反面有两种情况，1/8+1/8 =1/4。。

so a coin has two sides: heads or tails, so we are going to toss it up three times and we want the same side three times, that means we want either heads, heads, heads, or tails, tails, tails;

since getting a heads is 50% = 1/2, and get three heads in a row is: 1/2 * 1/2 * 1/2 = 1/8, in a similiar manner, to get three tails would be 1/8 as well, and since we can use both of three heads in a row and three tails in a row, we add them together: 1/8 + 1/8 = 1/4