There are 40 pages in a book. A page is opened at random. Find the probability that the number of this opened page is a multiple of 3 or 5

To solve this problem, we first need to find out how many pages are multiples of 3 or 5.

Step 1: Find the multiples of 3 within 40. The multiples of 3 within 40 are: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39. So, there are 13 pages that are multiples of 3.

Step 2: Find the multiples of 5 within 40. The multiples of 5 within 40 are: 5, 10, 15, 20, 25, 30, 35, 40. So, there are 8 pages that are multiples of 5.

Step 3: Find the common multiples of 3 and 5 within 40. The common multiples of 3 and 5 within 40 are: 15, 30. So, there are 2 pages that are multiples of both 3 and 5.

Step 4: Calculate the total number of pages that are multiples of 3 or 5. We add the number of multiples of 3 and 5, then subtract the number of common multiples (to avoid double-counting): 13 + 8 - 2 = 19 pages.

Step 5: Calculate the probability. The probability is the number of favorable outcomes (pages that are multiples of 3 or 5) divided by the total number of outcomes (total pages in the book). So, the probability is 19/40 = 0.475 or 47.5%.