We call a natural number "nice" if there are only even digits in its recording. How many "nice" four-digit numbers are there?

I suppose that this refers to numbers like:

N = abcd

Where a, b, c and d are single digits.

We want to find the number of 4-digit numbers such that:

a, b, c and d are even numbers.

So let's count the number of options for each digit, where we impose that the possible digits must be even.

a: Here we have the options {2, 4, 6, 8} ( 0 is an even digit, but if we take a = 0, then this would be a 3 digit number) Then we have 4 options for a.

b: Here we have the options {0, 2, 4, 6, 8}. 5 options in total.

c: Here we have the options {0, 2, 4, 6, 8}. 5 options in total.

d: Here we have the options {0, 2, 4, 6, 8}. 5 options in total.

The total number of possible combinations will be equal to the product of the number of options for each selection.

C = 4*5*5*5 = 500

There are 500 "nice" numbers of 4-digits.

"it's not the heat, it's the humidity".   that's a partly valid phrase you may have heard in the summer, but it's actually both.   the heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature.   this has important considerations for the human body's comfort.   when the body gets too hot, it begins to perspire or sweat to cool itself off.   if the perspiration is not able to evaporate, the body cannot regulate its temperature.   evaporation is a cooling process.   when perspiration is evaporated off the body, it effectively reduces the body's temperature.   when the atmospheric moisture content (i.e. relative humidity) is high, the rate of perspiration from the body decreases.   in other words, the human body feels warmer in humid conditions.   the opposite is true when the relative humidity decreases because the rate of perspiration increases.   the body actually feels cooler in arid conditions.   there is direct relationship between the air temperature and relative humidity and the heat index, meaning as the air temperature and relative humidity increase (decrease), the heat index increases (decreases).

step-by-step explanation: