Homework #8 solutions

HW #8, due Friday 4/7: 7.1 #2,3,7,9,11,13

7.1#2

Price held constant means staying in one column. The numbers increase as we go down, so that means beef consumption _increases_ with income.

#3

This just means replace each entry C in the column for price p by the product p*C (price*consumption = total amount spent).

#7

  • a) Same price cars, gas goes up -> people will buy fewer cars.
  • b) Same gas price, car prices go up -> people will buy fewer cars.
    • So both are decreasing.

    #9

    If we look down columns (fixed y, increasing x), the numbers decrease. If we look across rows (fixed x, increasing y), the numbers increase.

    #11

  • a) f(3,200) = 40*3 + 0.15*200 = 150. So, three days, 200 miles -> $150.
  • b) f(3,m) means we keep the car for definitely 3 days, but drive m miles. The graph is a straight line with slope 0.15.
  • c) f(d,100) means we keep it d days, driving exactly 100 miles. The graph is a straight line with slope 40 (nearly vertical).
    • #13
  • a) Last column, third row: -31.
  • b) First column, look for 22: it's in the 10 row.
  • c) Third column, look for 20: it's not there, being in between the 5 and 10 rows, very close to 5. Call it 5.5.
  • d) Third row, between the 25 and 20 columns: call it 23.