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3 years ago

Diameter = 18 cm

Mathematics

2 answers:

miskamm [114]3 years ago

7 0

Answer: B. 254.34 cm^2

Step-by-step explanation:

The area of a circle is pi times the radius squared.

Using the diameter we have to find the radius.

The diameter is two times the radius meaning that the radius is half the diameter.

18/ 2 = 9

The radius will be 9 cm

Now using the formula v= pi * r^2 , input the value for pie and the radius and solve for v the volume

v = 3.14 * 9^2

v= 3.14 * 81

v = 254.34 cm^2

marusya05 [52]3 years ago

4 0

Answer:

<em>The answer would be B) 254.34 cm2 </em>

Step-by-step explanation:

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3 years ago

A tank initially contains 60 gallons of brine, with 30 pounds of salt in solution. Pure water runs into the tank at 3 gallons pe

adoni [48]

Answer:

the amount of time until 23 pounds of salt remain in the tank is 0.088 minutes.

Step-by-step explanation:

The variation of the concentration of salt can be expressed as:

$\frac{dC}{dt}=Ci*Qi-Co*Qo$

being

C1: the concentration of salt in the inflow

Qi: the flow entering the tank

C2: the concentration leaving the tank (the same concentration that is in every part of the tank at that moment)

Qo: the flow going out of the tank.

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$\frac{dC}{dt}=-Co*Qo$

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$\frac{dC}{C}=-Qo*dt$

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$\int\frac{dC}{C}=\int-Qo*dt\\ln(\abs{C})+x1=-Qo*t+x2\\ln(\abs{C})=-Qo*t+x\\C=exp^{-Qo*t+x}$

It is known that the concentration at t=0 is 30 pounds in 60 gallons, so C(0) is 0.5 pounds/gallon.

$C(0)=exp^{-Qo*0+x}=0.5\\exp^{x} =0.5\\x=ln(0.5)=-0.693\\$

The final equation for the concentration of salt at any given time is

$C=exp^{-3*t-0.693}$

To answer how long it will be until there are 23 pounds of salt in the tank, we can use the last equation:

$C=exp^{-3*t-0.693}\\(23/60)=exp^{-3*t-0.693}\\ln(23/60)=-3*t-0.693\\t=-\frac{ln(23/60)+0.693}{3}=-\frac{-0.959+0.693}{3}= -\frac{-0.266}{3}=0.088$

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