So we know that we only have 450 people coming to the event.
When the guests arrive, will everybody have a place to sit?
Chairs: 0.6 * 600 = 360, not enough since there are still 90 people standing.
Will there be enough meals?
Meals: 0.6 * 600 = 360, not enough since there are 90 people who doesn't have meals.
Enough dessert?
Deserts: 0.625 * 600 = 375 , not enough since 75 people left with no desserts.