Only 235u can be used as fuel in a nuclear reactor, so uranium for use in the nuclear industry must be enriched in this isotope. if a sample of enriched uranium has an average atomic mass of 236.253 amu, what percentage of 235u is present?

Approximately 59.7739%.

Uranium has two naturally-occurring isotopes (note that despite the fact that both species are radioactive, they are the most abundant ones for having a relatively-long half-life.)

Assuming that of the uranium atoms in this sample are atoms of ; given the fact that other isotopes of uranium contribute to a negligible share of mass of the sample (less than in naturally-occurring samples,) would have contributed to of all atoms in this sample.

Similar to the standard atomic mass for an element, the average atomic mass of this sample shall resembles the atomic mass weighted over all atoms in the collection. Therefore