Chapter 1.01 part 2

If you see MTH/MTHT next to a problem, that means it is recommended just for Math majors/minors (MTH) and secondary-ed-math people (MTHT).
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QA: on page 13 section B, they say "a [mathematical model] is a function with an explicit formula . . ."; would you say that a math model has to be an explicit formula?

QB: For the postage cost problem on page 13, does 88+17*floor(w) accurately model the relationship between weight and cost?

QC: related to Example 9 and #67: 
i) sketch max(0,x); 
ii) sketch max(0,x-c); 
iii) sketch 0.10*max(0,x-10000); 
iv) sketch 40+0.21*max(0,x-500); 
v) sketch 0.10*max(0,x-10000)+0.08*max(0,x-30000)

QD: related to Example 9: 
i) Explain how max(0,1-abs(x-1)) reproduces the graph in example 9; 
ii) explain how x-2*max(0,x-1)+1*max(0,x-2) reproduces the graph in example 9; 
iii) If either of these doesn't exactly reproduce the graph in example 9, explain how to change it so it does.