What percent of the first 20 natural numbers are prime one-digit numbers?

We know that
Natural numbers are whole, non-negative numbers that are used for counting objects
A prime number is a natural number greater by 1, and which can be divided evenly by 1 or itself
A composite number is a whole number that can be divided evenly by numbers other than 1 or itself

see the attached picture to better understand the problem

in the first 20 natural numbers 
the prime one-digit numbers are-----> (2,3,5,7)----> total numbers  4

find the percent
20---------> 100%
4--------> x
x=4*100/20-----> x=20%

the answer is
20%