Let initially the number of passengers was x

Number of passengers after first halt = \( \Large \frac{x}{2}+125 \)

Number of passengers after second halt = \( \Large \frac{1}{2} \left(\frac{x}{2}+125\right) \)

By hypothesis,

\( \Large \frac{1}{2} \left(\frac{x}{2}+125\right)+100 = 250 \)

= \( \Large \frac{1}{2} \left(\frac{x}{2}+125\right)=150 \)

=> \( \Large \frac{x}{2}+125 = 300 \)

=> \( \Large \frac{x}{2} = 175 \)

=> x = 350