Question

1. a sample of element x is found to contain 72.15% of isotope type 1 (84.9118 amu) and 27.85% of isotope type 2 (86.9092 amu). calculate the average atomic mass.

Explanation:

Step1: Convert percentages to decimals

$72.15\% = 0.7215$, $27.85\%=0.2785$

Step2: Calculate the weighted - average

The average atomic mass $m = 0.7215\times84.9118+0.2785\times86.9092$
$m = 0.7215\times84.9118=61.3649637$
$0.2785\times86.9092 = 24.1042122$
$m=61.3649637 + 24.1042122=85.4691759\approx85.47$ amu

Answer:

85.47 amu