Answer:
24.83 hours
Step-by-step explanation:
Given that :
Let time taken by pumps be :
Pump A = 60 hours
Pump B = 80 hours
Pump C = 90 hours
Recall :
Rate = 1 / time taken
The rates of the pumps are :
Pump A rate = 1 / 60
Pump B rate = 1/80
Pump C rate = 1/90
Combined rate : 1/60 + 1/80 + 1/90
Combined rate = (12 + 9 + 8) / 720 = 29/720
Combined rate = 29/720
The time taken together will be :
1 / combined rate = 1/(29/720) = 720 / 29 = 24.827 hours
So,
3 CD's sell for $13.20 each.
3 * 13.20 = $39.60
$39.60 is also the price for 2 DVD's.
Divide $39.60 by 2.
$19.80
Each DVD is $19.80.
Well, there seven numbers to choose from. Out of the seven, four are even. The fraction for that is already simplified.
4/7
Essentially, what we're looking at here are two alternate interior angles.
Wait. What? Alternate interior angles?
It sounds like some super fancy math jargon, but it's a fairly simple concept that I'll try my best to explain. First, let's look at lines L and M as two parallel lines, meaning that these two are lines with equal slopes, and will never intersect. See that line that goes in between the parallel lines L and M? That's called a transversal. It's basically a line that goes through two parallel lines.
Now we know that there's a transversal going through the parallel lines. So what? Well, there's a couple of special attributes to transversals. See the two angles, 7x-7 and 4x+14? As you can tell, these two angles alternate in the interior space between the transversal and the parallel lines.
Alternate interior angles are equal. There's a way to prove that they're equal, but I won't bore you with the specifics since that's not what the question's asking.
If the angles need to be equal for lines L and M to be parallel, we can make an equation that'll solve for x:
7x - 7 = 4x + 14
<u>Subtract 4x from both sides:</u>
7x - 4 x - 7 = 4x - 4x + 14
3x - 7 = 14
<u>Add 7 to both sides:</u>
3x - 7 + 7 = 14 + 7
3x = 21
<u>Divide both sides by 3 to completely isolate x:</u>
= 
x = 7
And that's our answer! If you need me to explain anything any further, just ask!
- breezyツ