240(v+2.5)=1300-240v
240v+600=1300-240v
480v=1900
v=95/24
v-2.5=v-5/2
95/24-60/24=35/24
So the faster group travels at 95/24 mph (≈3.96 mph) and the slower group travels at 35/24 mph (≈1.46mph)
check...
240(95/24)=950 miles from the origin...
1300-240(35/24)=950 miles from the origin...
tis a little of plain differentiation.
we know the radius of the cone is decreasing at 10 mtr/mins, or namely dr/dt = -10, decreasing, meaning is negative.
we know the volume is decreasing at a rate of 1346 mtr/mins or namely dV/dt = -1346, also negative.
so, when h = 9 and V = 307, what is dh/dt in essence.
we'll be needing the "r" value at that instant, so let's get it

now let's get the derivative of the volume of the cone
![V=\cfrac{1}{3}\pi r^2 h\implies \cfrac{dV}{dt}=\cfrac{\pi }{3}\stackrel{product~rule}{ \left[ \underset{chain~rule}{2r\cdot \cfrac{dr}{dt}}\cdot h+r^2\cdot \cfrac{dh}{dt} \right]} \\\\\\ -1346=\cfrac{\pi }{3}\left[2\sqrt{\cfrac{307}{3\pi }}(-10)(9)~~+ ~~ \cfrac{307}{3\pi } \cdot \cfrac{dh}{dt}\right]](https://tex.z-dn.net/?f=V%3D%5Ccfrac%7B1%7D%7B3%7D%5Cpi%20r%5E2%20h%5Cimplies%20%5Ccfrac%7BdV%7D%7Bdt%7D%3D%5Ccfrac%7B%5Cpi%20%7D%7B3%7D%5Cstackrel%7Bproduct~rule%7D%7B%20%5Cleft%5B%20%5Cunderset%7Bchain~rule%7D%7B2r%5Ccdot%20%5Ccfrac%7Bdr%7D%7Bdt%7D%7D%5Ccdot%20h%2Br%5E2%5Ccdot%20%5Ccfrac%7Bdh%7D%7Bdt%7D%20%5Cright%5D%7D%20%5C%5C%5C%5C%5C%5C%20-1346%3D%5Ccfrac%7B%5Cpi%20%7D%7B3%7D%5Cleft%5B2%5Csqrt%7B%5Ccfrac%7B307%7D%7B3%5Cpi%20%7D%7D%28-10%29%289%29~~%2B%20~~%20%5Ccfrac%7B307%7D%7B3%5Cpi%20%7D%20%5Ccdot%20%5Ccfrac%7Bdh%7D%7Bdt%7D%5Cright%5D)
![-\cfrac{4038}{\pi }=-\cfrac{180\sqrt{307}}{\sqrt{3\pi }}+\cfrac{307}{3\pi } \cdot \cfrac{dh}{dt}\implies \left[ -\cfrac{4038}{\pi }+\cfrac{180\sqrt{307}}{\sqrt{3\pi }} \right]\cfrac{3\pi }{307}=\cfrac{dh}{dt} \\\\\\ -\cfrac{12114}{307}+\cfrac{180\sqrt{3\pi }}{\sqrt{307}}=\cfrac{dh}{dt}\implies -7.920939735970634 \approx \cfrac{dh}{dt}](https://tex.z-dn.net/?f=-%5Ccfrac%7B4038%7D%7B%5Cpi%20%7D%3D-%5Ccfrac%7B180%5Csqrt%7B307%7D%7D%7B%5Csqrt%7B3%5Cpi%20%7D%7D%2B%5Ccfrac%7B307%7D%7B3%5Cpi%20%7D%20%5Ccdot%20%5Ccfrac%7Bdh%7D%7Bdt%7D%5Cimplies%20%5Cleft%5B%20-%5Ccfrac%7B4038%7D%7B%5Cpi%20%7D%2B%5Ccfrac%7B180%5Csqrt%7B307%7D%7D%7B%5Csqrt%7B3%5Cpi%20%7D%7D%20%5Cright%5D%5Ccfrac%7B3%5Cpi%20%7D%7B307%7D%3D%5Ccfrac%7Bdh%7D%7Bdt%7D%20%5C%5C%5C%5C%5C%5C%20-%5Ccfrac%7B12114%7D%7B307%7D%2B%5Ccfrac%7B180%5Csqrt%7B3%5Cpi%20%7D%7D%7B%5Csqrt%7B307%7D%7D%3D%5Ccfrac%7Bdh%7D%7Bdt%7D%5Cimplies%20-7.920939735970634%20%5Capprox%20%5Ccfrac%7Bdh%7D%7Bdt%7D)
Answer:
24.6 % decrease
Step-by-step explanation:
Let x be the original temperature
Increase by 25%
x + .25x
1.25x
Decrease by 40%
The amount decreased is
(1.25x) *.40
.496x
Subtract that from 1.25x
1.25x - .496x
.754x
We need to find the percent decrease
1 - .754 = .246
24.6 % decrease