Final answer:
The cardinal number of set C = x is 15, as it includes all integers from 25 to 39.
Step-by-step explanation:
To find the cardinal number of set C = 25 ≤ x < 40, x ∈ ℤ, we need to identify all the integers between 25 and 40 (including 25 but not 40). Starting from 25, we can list the integers: 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39. These are the integers that satisfy the condition for set C, making a total of 15 elements. Thus, the cardinal number of set C is 15.
The cardinal number of a set refers to the number of elements in that set. In this case, the set C is defined as x , which means it contains all the whole numbers (ℤ) between 25 and 40, excluding 40. So, we need to count the number of whole numbers between 25 and 40.
This can be done by subtracting the lower limit (25) from the upper limit (40) and adding 1, because we need to include both endpoints:
40 - 25 + 1 = 16 + 1 = 17
Therefore, the cardinal number of set C is 17.