Answer
2.0 magnums
Work Step by Step
1 jeroboam
= 0.792 US gallons
= $ 0.792\; US\; gallons \times \frac{3.785\times 10^{-3}\; m^{3}}{1\; US\; gallon} \times \frac{1\; L}{10^{-3}\; m^{3}} $
$\approx$ 3.00 L
Number of magnums in a jeroboam
= 3.00 L $\div$ 1.5 L
= 2.0 magnums
