From the first place to the second place, passenger cars used to travel for 7 hours. After the opening of the expressway, the average speed increased by 20 kilometers per hour, so it only takes 5 hours to get there?

From the first place to the second place, passenger cars used to travel for 7 hours. After the opening of the expressway, the average speed increased by 20 kilometers per hour, so it only takes 5 hours to get there?

Let the original speed be x kilometers per hour
7x=(x+20)5
7x=5x+100
2x=100
x=50
Distance between a and B: 50x7 = 350 (km)

(1)2x+5y=19 (2）3x+5y=49k
3x+2y=12 3x-5y=-k
Quadratic equation of two variables (k is a constant)
Solving equations by adding and subtracting
Write this story

(1) 2X + 5Y = 19 times 3 6x + 15y = 57
3x + 2Y = 12 times 26x + 4Y = 24
By subtracting two from one, we get 11y = 33, y = 3, x = (12-6) / 3 = 2
(2）3x+5y=49k
3x-5y=-k
By subtracting two from one, we get 10Y = 50K, y = 5K
x= (-k+25k )/3= 8k

A and B leave from a and B at the same time. After meeting for 5 hours, B arrives at A. However, a exceeds B by 90 kilometers, 25% of the whole journey. How many kilometers does a travel per hour?

90 △ 25% = 360 (km) (360 + 90) △ 5 = 90 (km) 450:360 = 5:490 × 55 + 4 = 50 (km) a: car a runs 50 km per hour