Answer:

And we can find this probability using the normal standard table or excel and we got:

The figure shows the calculation for this case.
Step-by-step explanation:
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".
Solution to the problem
Let X the random variable that represent the hardness of a population, and for this case we know the distribution for X is given by:
Where
and 
We are interested on this probability

And the best way to solve this problem is using the normal standard distribution and the z score given by:

If we apply this formula to our probability we got this:

And we can find this probability using the normal standard table or excel and we got:

The figure shows the calculation for this case.
Answer:
The proportion that can be used to find x is;
(200-x)/x = 7/6
Step-by-step explanation:
Now, we want to find the proportion which can be used to find x.
From the question, we are told that the father skater traveled 7 ft for every 6 ft of the slower skater;
this means that the ratio of their speed is 7:6
Now, when they passed each other , the slower skater has traveled x ft, what this means is that the faster skater will have traveled a distance of (200-x) ft at that moment they passed each other.
Mathematically, since their time is equal i.e the time they used to pass each other, then, the ratio of their distances is same as the ratio of their speeds;
Hence;
(200-x)/x = 7/6 or x/(200-x) = 6/7
Answer: 40%
Step-by-step explanation: 20 hours jogging/ 50 total hours gives you .4 which is 40%