hello again.

i have a question i wonder whether some one will give a hint as to how best solve it ?

A vacuum pump removes 15% of the air that is in a container at the

beginning of a stroke. If

*m*r is the mass of air in the container after the *r *th

stroke:

(i) express

*m*2 and *m*3 in terms of the original mass *m*0

(ii) how many strokes are required to obtain 1% of the original mass?

so assuming mr is the mass of air after rth stroke i am assuming m2 must be the 2nd stroke =m1(15%) +m2,m3 must be m2 +m1 so we have a number series going on.

if mo is total air mass ie mo =100% can i express m2 and m3 as a percentage of mo ie m2 must equal 30% and m3 must equal 45% of mo respectively?not sure thats accurate enough.

qii. i will need to think more about,if every stroke assuming its in equilibrium removes 15% of air every time 100/15 =approx 7 strokes required to get to this point maybe thats also too simplistic.

apologies if i have got this in the wrong forum!