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 set up a proportion.
Let \( x \) be the amount of uranium-235 in kilograms used in the Tsar Bomba.
\[
\frac{1 \text{ pound of U-235}}{8000 \text{ tons of TNT}} = \frac{x \text{ kilograms of U-235}}{50000 \text{ tons of TNT}}
\]
Now, solve for \( x \). Cross-multiply and then divide:
\[
x = \left( \frac{1}{8000} \right) \times \left( 50000 \right) \times \left( \frac{1}{0.453592} \text{ kg per pound} \)
\]
This will give you the amount of uranium-235 in kilograms used in the Tsar Bomba.