Answer:
16. A whole number is always a natural number.
17. A fraction is sometimes a decimal.
19. An integer is sometimes a natual number.
20. A natural number is sometimes an integer. always a counting number. always a rational number.
Explanation:
16. A whole number is always a natural number.
Because whole numbers include 0 and positive numbers, and natural numbers are the numbers used to count and order things, therefore, a whole number is always a natural number.
17. A fraction is sometimes a decimal.
Because some fraction can give whole numbers and decimals as a result. Example of whole number: 50/2= 25, 25 is a whole number.
Example of decimal number: 3/2= 1.5, 1.5 is a decimal number.
19. An integer is sometimes a natual number.
Because integers are all whole numbers (positives and negatives) and 0, and natural numbers are only the positive numbers, those that can be used to count and order things.
20. A natural number is sometimes an integer. always a counting number. always a rational number.
Because integers are all whole numbers (positives and negatives) and 0, and natural numbers are only the positive numbers, those that can be used to count and order things. They are always rational numbers because can always be represented as the fraction of 2 integers.
Check the attatched image for a better understanding of the classification of numbers.