A bus arrives at a bus stop every 20 minutes. However, there is no set schedule for the bus, you just know that it does arrive every 20 minutes. You arrive at the bus stop not knowing when the last bus left. What is the probability that you will wait more than 15 minutes

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.