Question 1189270
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Answer:
*[Tex \LARGE C(x) = \left\{400 \ \text{ if } 0 \le x \le 20\\350 \ \text{ if } 20 < x < 30\\300 \ \text{ if } x \ge 30\\ \right. ]
x = number of students
C(x) = monthly cost for any one student


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How to get that answer:



The first line represents the portion {{{0 <= x <= 20}}}, ie when x is between 0 and 20 inclusive of both endpoints. If x is in this interval, then we can say C(x) = 400 since the teacher charges ₱400 when having between 0 and 20 students. This represents the cost for a single student (ie the amount the parent would pay if x fits the criteria). All throughout this sub interval, we have the cost stay the same.


Or if {{{20 < x < 30}}}, then we go for the middle option {{{C(x) = 350}}} (it's ₱50 cheaper per student in this interval). The reasoning is similar, but the interval is different this time of course. 


Or, we have one final option, if {{{x>=30}}} then {{{C(x) = 300}}} which is another ₱50 cheaper


So in short, the amount charged will have 3 tiers of {{{0 <= x <= 20}}} or {{{20 < x < 30}}} or {{{x>=30}}} which correspond to the charges of {{{400}}} or {{{350}}} or {{{300}}} in that order.
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