Question 500268
let the speed of the bus be x
increased by 10 
so speed = x+10

time with original speed - time with new speed = 1

300/x-300/(x+10)=1

LCD = x(x+10)

300*(x+10)-300x=x(x+10)
300x+3000-300x=x^2+10x
x^2+10x-3000=0
x^2+60x-50x-3000=0
x(x+60)-50(x+60)=0
(x-50)(x+60)=0
x=50 which is positive, the speed of the bus