Party A and Party B race to walk along the 400 meter playground. Party A walks 100 meters per minute and takes 80 meters per minute. Now Party A and Party B start from the same direction at the same time How many minutes does it take for two people to meet for the first time? How many laps did they walk? 2. How many minutes does it take for two people to meet for the second time?

Party A and Party B race to walk along the 400 meter playground. Party A walks 100 meters per minute and takes 80 meters per minute. Now Party A and Party B start from the same direction at the same time How many minutes does it take for two people to meet for the first time? How many laps did they walk? 2. How many minutes does it take for two people to meet for the second time?

I really can't think of it

Party A and Party B race along the playground. It is known that a circle of the playground is 400 meters. The speed of Party A is 100 meters per minute, and that of Party B is 80 meters per minute
(1) How many minutes does it take for them to meet for the first time? How many laps did they walk?
(2) How many minutes does it take for the second meeting?

Answer (1) 20 5 4
（2）20
What I'm thinking about is that two people start from the same direction. Let's set the time of two people's race walking as T. A's distance S = 100t, B's distance s' = 80t. A has to walk one more lap than B, so 100t-400 = 80t, t = 20 points
A: 100 * 20 / 400 = 5 B: 80 * 20 / 400 = 4 the second meeting took the same time as the first meeting

A warehouse is equipped with cement and a storehouse is the 2/5 of the second storehouse. 20 tons of inverted armour are transferred out of the second storehouse. At that time, a library is 75% of the B storehouse. How many tons of cement are there in the original B storehouse?

The original proportion of B in the total number is 1 (2 / 5 + 1) = 5 / 7
Later, Party B accounted for 1 / 7 of the total number (75% + 1) = 4 / 7
A total of 20 (5 / 7-4 / 7) = 140 tons
The original warehouse B is equipped with 140x5 / 7 = 100 tons

A car from a to B can arrive 0.5 hours in advance if it travels 80 kilometers per hour, and 0.5 hours later if it travels 60 kilometers per hour. How many hours does it take to arrive on time? How many kilometers are the two places apart?

(80 × 0.5 + 60 × 0.5) △ 80-60, = (40 + 30) △ 20, = 70 △ 20, = 3.5 (hours), 80 × (3.5-0.5), = 80 × 3, = 240 (kilometers). A: it takes 3.5 hours to arrive on time, and the distance between AB and ab is 240 kilometers