Chris walked the dog for 80 minutes or 1 hour and 20 minutes
Given:
Expression is

To prove:
If r is any rational number, then
is rational.
Step-by-step explanation:
Property 1: Every integer is a rational number. It is Theorem 4.3.1.
Property 2: The sum of any two rational numbers is rational. It is Theorem 4.3.2.
Property 3: The product of any two rational numbers is rational. It is Exercise 15 in Section 4.3.
Let r be any rational number.
We have,

It can be written as

Now,
3, -2 and 4 are rational numbers by property 1.
is rational by Property 3.
are rational by Property 3.
is rational by property 2.
So,
is rational.
Hence proved.
The theoretical probability of landing on tails is P = 0.5, and out of the 250 contestants, around 125 will win the game.
<h3>
About how many contestants will win?</h3>
The coin has two possible outcomes, so if it is a fair coin, the probability for each of the outcomes will be 0.5 (this is the theoretical probability for a fair coin, where all the outcomes have the same probability).
Now, we know that a person wins if the coin lands tails up, and the probability of landing on tails is 0.5
Then, for a sample N, we can expect that about 0.5*N of the participants win.
In this case, the sample is 250, then we can expect that:
0.5*250 = 125
Around 125 of the contestants win the game
If you want to learn more about probability, you can read:
brainly.com/question/251701