After the 1959 Toy Show, sales of the Barbie Doll took off, selling out the initial line of 500,000 and over a million outfits. Given this rate of unusually high sales and rapid popularity, many thought the product was a .

Suppose an economist believes that the price level in the economy is directly related to the money supply, or the amount of money circulating in the economy. the economist proposes the following relationship: p=a x m - p=price level - m=money supply - a=a composite of other factors, including real gdp, that change very slowly over time. how might an economist gather empirical data to test the proposed relationship between money and the price level? an economist would persuade the federal reserve to change the money supply to various levels, and observe the resulting changes in the price level. unlike researchers in the hard sciences, economists cannot study complex relationships using data. economists do not usually develop theoretical models of the economy but only analyze summary statistics about the current state of the economy. an economist would look for data on past changes in the money supply, and note the resulting changes in the price level

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Alarge tank is filled to capacity with 500 gallons of pure water. brine containing 2 pounds of salt per gallon is pumped into the tank at a rate of 5 gal/min. the well-mixed solution is pumped out at the same rate. find the number a(t) of pounds of salt in the tank at time t.