Estimated probability of guessing correctly on more than 3 out of 5 true-false questions

The probability of guessing 4 right is

... (5C4) * (1/2) ^5 = 5/32

The probability of guessing 5 right is

... (5C5) * (1/2) ^5 = 1/32

So, the probability of guessing 4 or 5 right is

... (5+1) / 32 = 6/32 = 0.1875