Luke buys 7 new pencils. Now he has 21 pencils. How many pencils did Luke have at first?
2 answers:
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Answer: 44 hours.
Step-by-step explanation:
Marisol is being paid $792.
We know that the job took her 8 hours more than she expected, so if we define T as the time she expected, this job took her:
T + 8 hours.
The amount of money per hour that she expected is calculated as:
$792/T = X
And for those 8 extra hours, she won $4 less per hour, then we have:
$792/(T + 8hs) = X - $4
Then we have a system of equations:
$792/T = X
$792/(T + 8hs) = X - $4
To solve this, we can notice that in the first equation X is isolated, then we could replace that in the second equation to get:
$792/(T + 8hs) = $792/T - $4
Now we can solve this for T.
$792 = ($792/T - $4)*(T + 8hs) = $792 + $792*(8hs/T) - $4*T + $32*hs
0 = $792*(8hs/T) - $4*T + $32*hs
Let´s multiply this both sides by T
0*T = ($792*(8hs/T) - $4*T + $32*hs)*T
0 = $792*8hs - $4*T^2 +$32*T*hs
This is a quadratic equation, where i will write this witout units so it is easier to read and follow:
0 = -4*T^2 + 32*T + 792*8
The solutions cab be found by using the Bhaskara´s formula, these are:
Then the solutions are:
T = (-32 + 320)/-8 = -36 hours (This is a negative time, and it does not really have a meaning in this problem, so we can discard this option)
The other solution is:
T = (-32 - 320)/-8 = 44 hours.
Then we can conclude that she expected the job would take 44 hours in total.