数學不會做

150 / x = 150 / (x+10) + 1/2
150 / x - 150 / (x+10) = 1/2
[150(x+10)-150x] / [x(x+10)] = 1/2
(150x+1500-150x) / (x^2+10x) = 1/2
2(1500) = x^2+10x
x^2+10x-3000 = 0
(x-50)(x+60) = 0
x= 50 or -60
therefore, the speed is 50km/h

proof:
original hours = 150 / x = 150 / 50 = 3 hrs
new hours = 150 / (x+10) = 150 / 60 = 2.5 hrs
original - new = 3 - 2.5 hr = 0.5 hr = 30 mins

(150)/(x+10) = (150/x)-0.5
(150)/(x+10) = (150-0.5x)/x
(x+10)(150-0.5x) = 150x
150x+1500-0.5x^2-5x = 150x
1500-0.5x^2-5x = 0
x^2+10x-3000 = 0
(x+60)(x-50) = 0

x = -60 or x = 50


速率不會是負數，所以此车辆的速率是50km/h