Question

If the total number of earthquakes annually averages 14,500 approximately how many are magnitude 5 or higher? and show work.

Answer 1

  To take a percentage of a number out, simply do the follow: 
Number x Percentage = Answer. 

Therefore: 
14,500x(90/100)=13,050 

To find what percentage a figure represents of a total, do the following simple equation: 
Figure/Total x100 = Percentage. 

So for your Earthquakes, you have a total of: 
Total = 90 + 20 + 5 + 1 = 116 Earthquakes. 

4 to 5 -> 90/116 x100 = 78% to 2 sig. fig. 
5 to 6 -> 20/116 x100 = 17% 
6 to 7 -> 5/116 x100 = 4% 
7+ -> 1/116 x100 = 1% 


The same technique is used everywhere else, sample size divided by total multiplied by 100 gives percentage. Not multiplying by 100 gives you a ratio of 1 that it represents, 1 being 100% (a complete unit). 
Therefore for part 1. of your question I would just do 14,500x0.9=13,050. 
You'll probably see that 90/100 = 0.9 since 90% is identical to writing 90/100 or 0.9.