[SHARMALA]

An element has two isotopes,P and Q.The ratio of percentage abundance of P to Q is 0.32.The isotopic mass of P and Q is 36.9695 and 34.9689,respectively.
(i)find the percentage abundance of isotope P and Q.
(ii)Determine the average atomic mass of the element. 

[Rutherford]

You should have written your attempt, but anyway, you have three unknowns, so you need three equations. Try to write those.

[SHARMALA]

hi..sori mr Raderford,i cant get the three equations...could you please help me?

[Rutherford]

Mark the unknowns with letters, for example, abundance of P is x₁, abundance of Q is x₂, the atomic mass is m_a. If you don't know the formula, here you can find it: http://en.wikipedia.org/wiki/Isotope#Occurrence_in_nature under paragraph "Atomic mass of isotopes".

[SHARMALA]

is it x=0.32 and x2=1-0.32

[Rutherford]

No, it is a ratio: x₁/x₂=0.32. You know also that abundances must add to 1 (or 100%). Here you have two equation with two unknowns. Solve them for x₁ and x₂, and you completed part (I). Then use the formula on the link for part (II).