Question 256397

A cylinder with a movable piston contains 2.00 g of helium, He, 

at room temperature. More helium was added to the cylinder 

and the volume was adjusted so that the gas pressure 

remained the same. How many grams of helium were added 

to the cylinder if the volume was changed from 2.00 L to 2.70 

L? (The temperature was held constant.)