Answer:
The speed is 60 mph.
Step-by-step explanation:
distance = 42 miles
Let he drove with speed v and time is t.
distance = speed x time
42 = v t ..... (1)
42 = (v + 10)(t - 1/10) ..... (2)
[tex]42 = 42 -\frac{v}{10}+ 10 t - 1\\\\t =\frac{10+v}{100}\\\\Put in (1)\\\\42 = \frac{v(10+v)}{100}\\\\v^2 + 10 v - 4200 = 0 \\\\v = \frac{-10\pm \sqrt{100+4\times 4200}}{2}\\\\v =\frac{- 10 \pm 130}{2}\\\\v =- 70 mph, 60mph[/tex]
So, the speed cannot be negative so the speed is 60 mph.
