Question

Eight sided dice can be described as two square based pyramids stuck together at

Answer 1

It costs $3.63 more for the gold die than the gold plated die.

The volume of each half of the die is given by the formula

V=1/3s³.

This means the total volume is V = 2(1/3s³) = 2(1/3(2³)) = 16/3 = 5.33 mm³.

For the solid gold die, we know that it weighs 0.02g per mm³:

5.33(0.02) = 0.1066g

Gold costs $40.38 per gram:
40.38(0.1066) = $4.30

For the plastic die, plastic weighs 0.01 g per mm³:
0.01(5.33) = 0.0533g

Plastic costs $10 per gram:
0.0533(10) = 0.533 ≈ $0.54.

We also need to find the surface area, as it will be painted.  Each face is an equilateral triangle; the area of a triangle is given by the formula

A = 1/2bh

We need to use the Pythagorean theorem to find the height.  The height will be one leg and 1/2 of the base will be the other; the slanted side will be the hypotenuse:

h² + (1/2(2))² = 2²
h² + 1² = 2²
h² + 1 = 4
h² = 3
h = √3

The area of the triangle would then be A = 1/2bh = 1/2(2)(√3) = √3.  There are 8 such faces on the die, so the total surface area would be 8√3 = 13.86mm².

Paint costs $0.01 per mm²:
13.86(0.01) = 0.1386 ≈ $0.14

Together the cost for the plastic is 0.14+0.53 = $0.67.

The difference between it and the cost for the gold die is 4.30 - 0.67 = $3.63.