A model for the food-price index (the price of a representative "basket" of foods) between 1984 and 1994 is given by the function

Question

I(t)=0.00009045t5+0.001438t4−0.06561t3+0.4598t2−.6270t+99.33

Where t is measured in years since midyear 1984, so 0≤t≤10, and I(t) is measured in 1987 dollars and scaled such that I(3)=100. Estimate to two decimal places the times when food was cheapest and most expensive during the 1984-1994 period.

Answer 1

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