From the book:
"About 1/3 of all plant and animal species in the United States are at risk of becoming extinct. There are 20,439 known species of plants and animals in the United States. How many species are at risk of extinction? (Source: The Nature Conservancy)"
Not so amusingly (being that I'm cramming), my solution results in 338,661 more species than there are known to be in the United States.
The steps I took to solve the problem are illustrated in figure 1. The steps I took to list all the prime factors of the number 20,439 are illustrated in figure 2. I made my notes as clear as possible.
Any hints regarding where I took a wrong step?