Answer:
Let V = the gas' volume and P = its pressure. Â The volume of a gas in a container varies inversely with the pressure on the gas:
Â
  V = k/P
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where  k is a constant.  To find the value of k, plug in the one known point, V = 390 cubic inches when P = 7 pounds per square inch and solve for k:
Â
  V = k/p
  390 = k/7
  390*7 = k
  2730 = k
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The full equation, then, is:
Â
  V = 2730/P
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To find the volume when P = 9 pounds per square inch:
Â
  V = 2730/9 = _____ cubic inches
Step-by-step explanation:
Let V = the gas' volume and P = its pressure. Â The volume of a gas in a container varies inversely with the pressure on the gas:
Â
  V = k/P
Â
where  k is a constant.  To find the value of k, plug in the one known point, V = 390 cubic inches when P = 7 pounds per square inch and solve for k:
Â
  V = k/p
  390 = k/7
  390*7 = k
  2730 = k
Â
The full equation, then, is:
Â
  V = 2730/P
Â
To find the volume when P = 9 pounds per square inch:
Â
  V = 2730/9 = _____ cubic inches