Question 897554
Let x be that unknown number.


We have this set of numbers: 93,84,86,75,x


We want the mean of them to be equal to 86, so (93+84+86+75+x)/5 = 86. Notice how I added up all the numbers and divided by 5 (there are 5 numbers in the set 93,84,86,75,x)


Solve for x to get...


<pre>
	(93+84+86+75+x)/5 = 86

	93+84+86+75+x = 5*86

	93+84+86+75+x = 430

	338+x = 430

	x = 430-338

	x = 92
</pre>

So the answer is 92