If 1 pound of uranium-235 has the same explosive power as 8,000 tons of TNT, and you want to find out how much uranium-235 was used in the Tsar Bomba (50 MT or megatons), you can use the given ratio.
Let \( x \) be the amount of uranium-235 in kilograms used in the Tsar Bomba.
\[
\frac{{1 \, \text{pound U-235}}}{{8,000 \, \text{tons TNT}}} = \frac{{x \, \text{kg U-235}}}{{50,000 \, \text{tons TNT}}}
\]
Now, solve for \( x \):
\[
x = \left( \frac{1}{8,000} \right) \times \left( 50,000 \right) \times \left( \frac{1}{0.453592} \right)
\]
This will give you the amount of uranium-235 in kilograms used in the Tsar Bomba.