A combination lock has 40 numbers from zero to 39, and a combination consists of 3 numbers in a specific order with no repeats. Find the probability that the combination consists only of even numbers. (Round your answer to three decimal places.) The probability that the combination consists only of even numbers is

Step 1 ：First, we need to calculate the total number of combinations possible with 40 numbers taken 3 at a time. This is given by the formula for permutations, which is nPr = n! / (n-r)!, where n is the total number of items, r is the number of items to choose, and '!' denotes factorial. In this case, n = 40 and r = 3.

Step 2 ：Using the formula, we find that the total number of combinations is 59280.

Step 3 ：Next, we need to calculate the number of combinations possible with only even numbers. There are 20 even numbers from 0 to 39, so we use the same formula with n = 20 and r = 3.

Step 4 ：Using the formula, we find that the number of even combinations is 6840.

Step 5 ：The probability is then the number of even combinations divided by the total number of combinations.

Step 6 ：Calculating the probability, we get approximately 0.115.

Step 7 ：Final Answer: The probability that the combination consists only of even numbers is approximately \(\boxed{0.115}\).