Interesting Mathematics in Grade Four (Mathematics Wide Angle)

1. Someone's house number is four digits. One day, when he was doing a handstand outside the door, he found that their house number was turned upside down into another four-digit number, and it was 4872 bigger. What's this man's house number?

There are ten apple frames, each frame has 50 apples, and the apples in each frame are the same weight. Now it is known that the total weight of nine frames of apples is 50 kg (that is, each apple weighs 1 kg), and the total weight of another frame of apples is 45 kg (that is, each apple weighs 9 times). Now only one weighing is allowed. How can I find out which frame of apples are 9 two?

Now Xiaoming's family has crossed a bridge. It's dark when crossing the bridge, so there must be a light. Now it takes 1 second for Xiaoming to cross the bridge, 3 seconds for Xiaoming's brother, 6 seconds for Xiaoming's father, 8 seconds for Xiaoming's mother and 12 seconds for Xiaoming's grandfather. At most two people can cross the bridge at a time. The speed of crossing the bridge depends on the slowest one. The light turns on for 30 seconds and then goes out. Ask Xiaoming how to cross the bridge.