Question

a small bar of gold is a rectangular prism that measures 40 millimeters by 25 millimeters by 2 millimeters. one cubic millimeter of gold weighs about 0.0005 ounce. Find the volume in cubic millimeters and the weight in ounces of this small bar of gold.

Answer 1

Step One 
Find the Volume in ccs.

V= l*w*h
l =40 mm
w = 25 mm
h = 2 mm
V = 40*35 * 2
V = 2800 mm^3

Step Two
Find the weight
1  mm^3 = 0.0005
2800 mm^3 = x   <<<<< answer 1

$\frac{1}{2800} = \frac{0.0005}{x}$   Cross multiply.

1x = 2800 * 0.0005
x = 1.4 ounces.  <<<<< answer 2