Question

$5 coin diameter: 2.5 cm

Answer 1

The total surface area of a coin can be solve by using this formula
Surface Area = Area Front + Area Back + Area Side
Surface Area = 2Area Front/Back + Area Side

The Area of the Front and Back of the coin can be solve by using the formula of a circle which is $A= \pi (d/2)^{2}$

And the Area of a Side of the coin can be solve by using the formula
A = πd x thickness

We will solve first the surface area of a $5 coin.
note: 2.5 cm = 25 mm

Surface Area = 2(π(d/2)^2) + πd x thickness
                       = 2(π(12.5)^2) + 25π x 3
                       = 2 (156.25π) + 75π
                       =312.50π + 75π
                       = 387.50π
Surface Area of $5 coin is 387.50π sq mm

We will next solve for surface area of a 50 cents.
note: 2 cm = 20 mm
Surface Area = 2(π(d/2)^2) + πd x thickness
                       = 2(π(10)^2) + 20π x 1.5
                       = 2 (100π) + 30π
                       = 200π + 30π
                       = 230π
The surface area of a 50 cents is 230π sq mm.

Therefore, the ratio of the total surface area of $5 coin to 50 cents is
387.50π sq mm : 230π sq mm