What is the average atomic mass of 125 atoms of uranium if there are 10 atomd of u-234, 75 atoms of u-235, and 40 atoms of u-238?

Answer is: the average atomic mass of 125 atoms of uranium is 235.88.

ω(U-234) = 10 ÷ 125.

ω(U-234) = 0.080.

ω(U-235) = 75 ÷ 125.

ω(U-235) = 0.60.

ω(U-238) = 40 ÷ 125.

ω(U-238) = 0.320.

Average atomic mass of atoms of uranium =

Ar(U-234) · ω(U-234) + Ar(U-235) · ω(U-235) + Ar(U-238) · ω(U-238).

Average atomic mass of atoms of uranium =

234 · 0.08 + 235 · 0.6 + 238 · 0.32.

Average atomic mass of atoms of uranium = 18.72 + 141 + 76.16.

Average atomic mass of atoms of uranium = 235.88.