You have two unknown rates, so we need to develop two equations to solve for these unknowns (based on the information given on the problem statement):
5x + 10y = 725
x + y = 100
By substitution, we get:
5x + 10(100 - x) = 725
5x + 1000 - 10x = 725
-5x = 725 - 1000
-5x = -275
x = -275/-5 = 55
100 - 55 = 45
Thus:
The mechanic who worked for 5 hours charged his time at $55/hr, and the mechanic who worked for 10 hours charged his time at $45/hr.
To verify, plug and chug the results back into the original equations:
5(55) + 10(45) = 725
275 + 450 = 725
725 = 725 [OK]
55 + 45 = 100 [OK]
Answer:
The first incorrect justification is in step 2.
Step-by-step explanation:
<u>Step 2</u>. BC2 = AC • DC
2. BC ÷ DC = BC ÷ AC because triangle ABC is similar to triangle BDC
It's supposed to be AC ÷ BC not BC ÷ AC.
I've attached a plot of one such cross-section (orange) over the region in the x-y plane (blue), including the bounding curves (red). (I've set

for this example.)
The length of each cross section (the side lying in the base) has length determined by the horizontal distance

between the y-axis

and the curve

. In terms of

, this distance is

. The height of each cross section is twice the value of

, so the area of each rectangular cross section should be

.
This means the volume would be given by the integral
500 = 10x + 2 * 15 * 5 + 15x
500 = 25x + 150
500 - 150 = 25x
350 = 25x
x = 14
Triangular ends: 14 * 10 = 140
Base rectangle: 14 * 15 = 210
side rectangles: 5 * 15 * 2 = 150
140 + 210 + 150 =