The closing price of Stock ~$X$~ changed on each trading day last month. The percent change in the closing price of Stock ~$X$~ from the first trading day last month to each of the other trading days last month was less than 50 percent. If the closing price on the second trading day last month was $10.00, which of the following CANNOT be the closing price on the last trading day last month?
$3.00
$9.00
$19.00
$24.00
$29.00
解答:设第一天的closing price为F,
当这个change是第一天的增加50%才是第二天的closing price
所以:F(1+50%)=10
F=6.67
当这个change是第一天的减少50%才是第二天的closing price
所以:F(1-50%)=10
F=20
因此第一天的closing price范围是(6.67,20)
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