If you would like to know how many hours will Lena need to work before she can afford to buy the computer, you can calculate this using the following steps:
$900 - $473 = $427
$427 / $7 = 61 hours of yard work
Result: Lena will need to work 61 hours before she can afford to buy the computer.
Cost of the computer that Lena wants to buy = 900 Amount of money saved by Lena = $473 Amount per hour paid by Lena's grandmother = $7 Let us assume the number of hours Lena have to work = x Then 473 + 7x = 900 7x = 900 - 473 7x = 427 x = 427/7 = 61 So Lena has to work 61 hours before she can afford top buy the computer.I hope the procedure is clear enough for you to understand.
if the mean is 70 minutes, then 90 minutes is 2 standard deviations above 70. if you look at the bell curve i drew, the percent of exams that took over 90 minutes is 2.5%
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