[turinturambar]

Hey, I am new to this forum site. My apologies if this sounds pretty elementary to anyone on here, I am studying a Biology degree but have a Chemistry module and really would like to see if there is anyone that could explain certain questions to me so that I can gain an understanding into key concepts I will be covering in my chemistry module.

The first 2 questions I wanted to share are as follows:
 

• Naturally occurring copper (Cu) has a relative atomic mass of 63.54 and consists of a mixture of isotopes of mass numbers 63 and 65. In what proportions do these isotopes exist? (Hint: let the percentage of 63Cu be x. The percentage of 65Cu will therefore be (100 – x). The form of the calculation is exactly as in questions 2 and 3, but the unknowns now are the percentages rather than the relative atomic mass.)

I have the answer but I am trying to understand how I use x I just want to understand the basic process so I can try and solve other problems like this one

• Naturally occurring boron consists of a mixture of two isotopes: 10B and 11B. The relative atomic mass of boron is 10.81, so what does this tell us about the relative proportions of the two isotopes? I also have the answer for this but the same applies
  
  I am just trying to wrap my head around it, I apologise if I am a bit vague. I haven't done maths for almost 10 years and I have just started a degree without expecting chemistry and maths to be involved XD
  
  Thanks for reading!!
  

[Borek]

Do you know what the weighted average is?

[NDW]

The x is used so that we can discuss two different things without using two variables.

If apples = a
carrots = t

and we know that there are 10 times more carrots than apples, then we can say that t = 10a and eliminate the t variable all together.

apples = a
carrots = 10a