Question 1102716
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Your statement of the problem doesn't make it clear; but in fact this function is a step function.  The given data points tell us
1 ounce --> 49 cents
2 ounces --> 70 cents
3 ounces --> 91 cents
3.5 ounces --> $1.12<br>
The first three data points make this look like a linear function -- specifically, {{{C = 28+.21x}}} where x is the weight in ounces of the letter.  However, the cost of mailing a letter weighing (for example) 2.35 ounces is 91 cents, not 28+2.35(21)=77.35 cents.<br>
The step function (a piecewise function) giving the cost of postage for mailing a letter weighing between 0 and 3.5 ounces is
C = .49, if 0<=x<1;
C = .70, if 1<=x<2;
C = .91, if 2<=x<3;
C = 1.21, if 3<=x<=3.5<br>
You could write this function without using a piecewise function by using the floor function, where floor(x) is the largest integer less than or equal to x:
C = .49 + .21*floor(x)