Question 1098429
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<pre>
70% is exactly 0.7.


Therefore, your condition says:  0.7x = 210.


Then x = {{{210/0.7}}} = 300.
</pre>


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Specially for you, there is a bunch of lessons on percentage problems 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/percentage/lessons/Percentage-problems.lesson>Percentage problems</A> (*)

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Percentage-and-ratio-word-problems/Percentage-word-problems-%28Type-1-problems-Finding-the-Part%29.lesson>Percentage word problems (Type 1 problems, Finding the Part)</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Percentage-and-ratio-word-problems/Percentage-word-problems-%28Type-2-problems-Finding-the-Rate%29.lesson>Percentage word problems (Type 2 problems, Finding the Rate)</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Percentage-and-ratio-word-problems/Percentage-word-problems-%28Type-3-problems-Finding-the-Base%29.lesson>Percentage word problems (Type 3 problems, Finding the Base)</A> (**)

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Percentage-and-ratio-word-problems/More-complicated-percentage-problems.lesson>More complicated percentage problems</A>

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Percentage-and-ratio-word-problems/Problems-on-percentage-that-lead-to-unexpected-results.lesson>Problems on percentage that lead to unexpected results</A>

in this site.



Read them and become an expert in this area.
Start with the lesson (*), then continue with the lesson (**).