Let's begin by listing out the information given to us:
There are four students: n = 4
Number of students to be selected: r = 2
To calculate the combination of 2 students to be chosen, we use:

Therefore, there 12 possible combinations from these
Answer:
10×4 = 40
10^4 = 10,000
Step-by-step explanation:
10^4 is another way to write 10⁴ = 10·10·10·10 = 10,000.
Essentially, the exponent tells you how many places to the right of the leading digit the decimal point lies (here, the number of zeros in the number).
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<em>Comment on the answer choice</em>
The appropriate answer depends on what you mean by your problem statement. Some microscopes magnify 40 times; others magnify 10,000 times, so we cannot tell the appropriate answer using our knowledge of microscopes.
Basically a proportion so it’d be 1in/300 mi = 3in/x mi
cross multiple that out and you get 300•3=x and then just solve for x. the answer should be 900 miles.
You can use any letter but when you label it x you find x