A whole number is added to a number with two didgets after the decimal point. To make sure the answer is reasonable, how many didgets should the sum have after the decimal point ?

A - none
B - 1
C- 2
D- infinitely many

C - 2

To determine how many digits the sum should have after the decimal point, we need to understand what happens when we add a whole number to a number with two digits after the decimal point.

Let's consider an example:

Whole Number: 5
Number with two decimal digits: 3.14

When we add these two numbers together (5 + 3.14), we get 8.14. The sum has the same number of digits after the decimal point as the original number with two decimal digits (3.14).

This example suggests that when we add a whole number to a number with two decimal digits, the sum should have two decimal digits as well.

Therefore, the correct answer is C - 2.