methane gas is compressed from 20. L to 2.5 L at a constant temperature. The final pressure is 12.2 atm. What was the original pressure?

this is chemistry but ok first the equation is P1 V1 = P2 V2 boyle's law
plug in the numbers
P1 (20) = (12.2atm)(2.5)

P = 1.525 atm

rounded to 2 sig figs:
1.5 atm

Using p1*v1 = p2*v2 we have  p1*20 = 12.2*2.5 so p1 = 12.2*2.5/20

$${\mathtt{p1}} = {\frac{{\mathtt{12.2}}{\mathtt{\,\times\,}}{\mathtt{2.5}}}{{\mathtt{20}}}} \Rightarrow {\mathtt{p1}} = {\mathtt{1.525}}$$ atm

dang alan i was working so hard on this one.......but yeah thats right

I've given you a thumbs up, zegroes!

lol thanks alan