To find the probability, we must determine the total number of possible five-digit numbers and the number of five-digit numbers divisible by 5. The probability is the ratio of these two values.
Step 1: Total Possible OutcomesA five-digit number cannot start with the digit 0. The digits available are {0,1,2,3,4,5,6}, a total of 7 digits. We must form a five-digit number without repetition.
• For the first digit (ten thousands place), there are 6 choices (1, 2, 3, 4, 5, 6).
• For the second digit, there are 6 choices (any of the remaining 6 digits, including 0).
• For the third digit, there are 5 choices.
• For the fourth digit, there are 4 choices.
• For the fifth digit, there are 3 choices.
Total possible numbers = 6×6×5×4×3=2160
Step 2: Favorable OutcomesA number is divisible by 5 if and only if its last digit is either 0 or 5. We must consider two separate cases.
Case 1: The last digit is 0.
• The last digit has 1 choice (0).
• The first digit can be any of the remaining 6 digits.
• The second digit has 5 choices.
• The third digit has 4 choices.
• The fourth digit has 3 choices.
Number of possibilities = 6×5×4×3×1=360
Case 2: The last digit is 5.
• The last digit has 1 choice (5).
• The first digit cannot be 0 or 5. So, there are 5 choices (1, 2, 3, 4, 6).
• The second digit has 5 choices (including 0 now).
• The third digit has 4 choices.
• The fourth digit has 3 choices.
Number of possibilities = 5×5×4×3×1=300
Total favorable numbers = 360+300=660
Step 3: Find the Probability
Required probability = # of Favorable Outcomes / Total Possible Outcomes = 660 / 2160 = 11/36
Hence
choice (D) is right.