A mystery element "X” has two stable isotopes X-50 which occurs 40% of the time and X-60 which occurs 60% of the time. What is the average mass of element "X"?

A-50 amu
B-54 amu
C-56 amu
D-60 amu

B? i feel like this is a trick  

The disturbance is only parallel to the motion of the wave.

This question is rather vague, but i will try and answers it as best i can.start by being polite, then complement on the attributes that you like about that person. be friendly to her friends. don't be mean to anybody she knows, even if you really don't like them. be yourself, don't try to impress, just be yourself and hope that she likes you.