005 Weight of ivory billiard balls

Unit weight of ivory
$\gamma = 114 \, \text{lb/ft}^3$
 

Volume of one billiard ball
$V_1 = \frac{1}{6}\pi d^3 = \frac{1}{6}\pi (2.5^3)$

$V_1 = 8.18123 \, \text{ in}^3$
 

Volume of 1000 billiard balls
$V = 1000V_1 = 1000(8.18123)$

$V = 8181.23 \, \text{ in}^3 = 8181.23 \, \text{ in}^3 \left( \dfrac{1 \, \text{ ft}}{12 \, \text{ in}} \right)^3$

$V = 4.7345 \, \text{ ft}^3$
 

Weight of 1000 billiard balls
$W = \gamma V = 114(4.7345)$

$W = 539.73 \, \text{ lb}$           answer