1 and 5 minutes later, the distance between sisters is 5*( 100+80)=900 meters.

It takes 900/( 100-80)=45 minutes for an elder sister to catch up with her younger sister.

Sister always walks for 5+45=50 minutes.

So my sister walked 50 * 100 = 5000m.

After 2.30 minutes, the distance between them is 30*20=600 meters.

So Xiaoping went to the Children's Palace, and Xiaohong walked 600-350=250 meters.

Xiaoping walked 100 meters longer than Xiaohong, and it took 100/20=5 minutes.

So Xiaohong walks 250/5=50 meters every minute.