<PRE><B>Question 1161813</B>
&lt;br&gt;
Informally....&lt;br&gt;
The difference in cost per shirt is Php 5; the difference in the setup fee is Php 250.  The number of shirts to make up the difference in setup fee is 250/5 = 50.&lt;br&gt;
So the price will be the same if 50 shirts are printed.&lt;br&gt;
That means if the number of shirts is greater than 50 the service with the lower cost per shirt should be used; if the number is less than 50, the service with no setup fee should be used.&lt;br&gt;
Assuming a separate order for the different grades is to be made, it is clear that one service should be used for some grades and the other service for other grades -- and that the cost for the shirts for grade 8 will be the same with either service.&lt;br&gt;
Formally....&lt;br&gt;
1.&lt;br&gt;
{{{y = 50x}}}
{{{y = 45x+250}}}&lt;br&gt;
2. Use substitution.  You want to find when the cost of the two services is the same; the two equations show different expressions that are both equal to y.  So write the equation that says those two expressions are equal:&lt;br&gt;
{{{50x = 45x+250}}}&lt;br&gt;
3. Solve the equation from 2. to find the number of shirts x that makes the cost the same for both services.&lt;br&gt;
Then use the service with the lower cost per shirt if the number of students in a grade is more than x, or use the service with no setup fee if the number of students is less than x.&lt;br&gt;
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