[philonossis]

"the following isotopic mass ratios were determined experimentally:

¹⁹₉F/¹²₆C= 1.5832          
³⁵₁₇CL/¹⁹₉F= 1.8406  
⁸¹₃₅Br/³⁷₁₇Cl = 2.3140

Based on this information, what is the mass of ⁸¹₃₅Br in atomic mass units?"

My method:
1. create a relative scale where C=1.

C....F.....Cl.....Br
1....1.5832.....2.91407....6.74308

2. multiply each value by the one next up:

I got the answer 80.917, just out of desperation because I could not figure out the method.  This was also the book's answer.  But it seems to me it should be wrong because we are jumping from one isotope of Cl (mass 35) to another (mass 37).

Is it correct not to factor in the extra two neutrons?

[Schrödinger]

I think the book meant Cl-35, since the answer given in the book agrees with it. Probably a typo

You can check :
19/12 = 1.583
35/19 = 1.84
81/35 = 2.314
81/37 = 2.189

[philonossis]

I think the book meant Cl-35, since the answer given in the book agrees with it. Probably a typo
.

thanks for doing this checking.