Please explain?

In the morning, John drove to his mother's house in the village at an average speed of 60 kmh. When he was going back to town in the evening, he drove more cautiously and his speed was lower. If John went the same distance in the evening as in the morning, what was John's average speed for the entire trip?

1.In the evening, John drove at a constant speed of 40 kmh.

2.John's morning drive lasted 2 hours.

If A ,B and C are points on the plane, is AB<10 ?

1. AC +BC =10

2. AB + AC > 10

How much water (in grams) should be added to a 35%-solution of acid to obtain a 10%-solution?

1.There are 50 grams of the 35%-solution.

2.In the 35%-solution the ratio of acid to water is 7:13.