The profit that John got from the last 50 was $5000.
Answer: Choice D

Reason:
Whenever we have two lines cross to form an X shape, the vertical angles are always opposite one another. They do not have to be vertically stacked (as they can be side by side like angles 2 and 4 are). Vertical angles are always congruent.
6.665 grams of the 13 grams remain after 8 hours.
<h3>How much of a 13 gram sample of iron-52 would remain after 8 hours?</h3>
The decay equation for the 13 grams of iron-52 is:

Where N is the amount of iron-52, and t is the time in years.
Where we used the fact that the half-life is exactly 8.3 hours.
Now, the amount that is left is given by N(8h), so we just need to replace the variable t by by 8 hours, so we get:

So 6.665 grams of the 13 grams remain after 8 hours.
If you want to learn more about half-life:
brainly.com/question/11152793
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Answer: 2 19/24 hours was spent in practising.
Step-by-step explanation:
During the first hour, they practiced for 5/8 of an hour. During the second hour, they practiced for 2/3 of an hour. This means that the total time for which they practiced in the first 2 hours would be
5/8 + 2/3 = 31/24 hours
During the last two hours, they first practiced for 3/5 of an hour, took a 1/2 hour break and then practiced the rest of the time. This means that the rest of the time for which they practiced is
2 - (3/5 + 1/2) = 2 - 11/10 = 9/10
Therefore, the time they spent practicing in total would be
31/24 + 3/5 + 9/10 = 67/24 =
2 19/24 hours