The following problems I answered wrong. DO not understand how the instructor go
ID: 3342189 • Letter: T
Question
The following problems I answered wrong. DO not understand how the instructor got his answer. Please help with full calculations please.
1) Fly-by-Night Airlines requires that the length plus width of a carry-on bag not exceed 41 inches and the width plus height must also not exceed 41 inches. What is the width of the carry-on bag that has the largest volume?
My answer = 20.5 (WRONG) Correct answer = 13.67 (?)
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2) A new house is built across the river which is 229 yards downstream from the nearest telephone relay station. The river is 90 yards wide. In order to wire the house for phone service, wire will be laid across the river under water and along the edge of the river above ground. The cost to lay wire under water is $29 per yard and the cost to lay wire above ground is $12 per yard. How much wire should be laid ON LAND to minimize the cost?
My answer = 139 (WRONG) Correct answer = 188.09 (?)
Explanation / Answer
let length=l
width=d
height=h
l+d<=41
d+h<=41
volume=v=l*d*h
=(41-d)*d*(41-d)
dv/dd=0
solving for the equation,we get
d=41/3=13.67 in
2)let length of wire on land be l.
then length under water=sqrt(90^2+(229-l)^2)
so total cost=C=12*l+29*sqrt(90^2+(229-l)^2)
dC/dl=0
solving for above equation,we get
l=188.1 yards
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