Which number between 20 and 28 are prime

Prime numbers basically numbers that dont have any numbers that will be multiplied to get to it. So, it would be:
 23
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All the other numbers in between can be divided by something and not become a decimal. Other than 23, it can be divided by anything without becoming a decimal.

~Hope this helped :)

 The number is 23, that is the only number prime between 20 and 28

Volume of cylinder(V) is given by:

           ....[1]

where, r is the radius of the cylinder and h is the height of the cylinder

From the diagram:

Diameter of a pipe (d) = 10 cm

height of the pipe(h) = 2m    

Use conversion:

1 m = 100 cm

then

2m  = 200 cm

⇒h = 200 cm

Since, a pipe is in the form of cylinder.

We have to find the volume of a pipe.

We know that:

⇒

Divide both sides by 2 we get;

5 = r

or

r = 5 cm

Substitute the given values and use  π = 3.14. in [1] we have;

Simplify:

Therefore, the volume of a pipe in cm³ is, 15700