chemistry
posted by lyne on .
The element rhenium (Re) has two naturally occurring isotopes, 185Re and 187Re, with an average atomic mass of 186.207 amu. Rhenium is 62.60% 187Re, and the atomic mass of 187Re is 186.956 amu. Calculate the mass of 185Re.
am i supposed to multiply the atomic masses and the percents or something?
im lost..

yes. Both multiply AND something.
0.6626*X + 0.3740(186.956) = 186.207
Make sure I have these paired right.
X stands for amu Re185. Solve for X. 
You can check your answer this way.
Multiply decimal percent of amu 185 and decimal percent of amu 187, add them together and you should get 186.207. 
shouldnt it be .626(186.956)+.374*X=186.207

yes, I don't know why I typed in 6626. It should be 0.626 and 0.374. Neither do I know why I reversed the order when I typed it in BUT I'm glad I put in the post to check my pairings. According to my notes, I have
0.374(X) + 0.626(186.956) = 186.207 which I think agrees with what you have.
My eyesight is not that great as you can tell. 
x=186.207(0.626)(186.956)/0.374=184.953

where is the 0.3740 coming from

The 0.374 comes from taking 100 percent and subtracting the 62.60% from it which gives you 37.4 percent, divide by 100 to get 0.374, now multiply by x and solve as listed above.