



 
Hi Kenneth, What you did is correct but I think it is advantageous to use a variable, especially for the two questions you asked. In your first example let $X$ be the unknown quantity then you could write your solution as
Two more observations. Firstly the word "of" in this situation indicates multiplication as in
or
Secondly "percent" means per 100 so, for example 4% is $\large \frac{4}{100}.$ Back to your question 16 is ?% of 400. You have used "?" for the unknown quantity so I'll stick to that and your question becomes \[16 = \frac{?}{100} \times 400\] or \[16 = ? \times 4 \mbox{ and hence } ? = 4.\] and your second question ? is 4% of 400 becomes \[? = \frac{4}{100} \times 400 = 4 \times 4 = 16.\] I hope this helps,  


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