Answer: 25%
Step-by-step explanation: Since we know that David has 20 pencils in all and that 5 of the pencils he has are green, we have the fraction 5/20 which represents the 5 green pencils out of all of his pencils.
Now, remember the problem is looking for a percent so we need to write 5/20 as a percent in order to answer the question.
To write a fraction as a percent, first remember that a percent is a ratio of a number to 100. So to write 5/20 as a percent, we need to find a fraction equivalent to 5/20 that has a 100 in the denominator. We can do this by setting up a proportion.
Now, we can use cross products to find the missing value.
So we have 5 times 100 which is 500 is equal to 20 times n or 20n.
So we have 500 = 20n.
Now, dividing both sides of the equation by 20, we have 25 = n.
So 5/20 is equal to 25/100 or 25%.
Therefore, 25% of David's pencils are green.