MODEL: The average density of the rock is its mass divided
by its volume (equation 13.1).

SETUP: We'll need to express the total mass *M* in terms of the mass of basalt and the mass of air. Express both in terms of the unknown fraction*f*_{air} of the rock's volume that is occupied by the bubbles.
SOLVE: Set your expression for the rock's density equal to the density of pumice computed from its given total mass of 10 kg and total volume.
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© 1998 Susan M. Lea