Question

frankie Kowalski drove his jeep for 135moles on a paved road. he decreased his speed by 25 mph when he went on a dirt road. He traveled for 40 miles on the dirt road. If frankie drove his jeep for 5 hours, what was his speed when driving on the paved road?​

Answer 1

45 miles per hour

Explanation:

Time taken is given by distance/speed

Let speed on paved road be x hence on dirt road x-25

Time on paved road is
`\frac {135}{x}`

Time on dirt road is
`\frac {40}{x-25}`

The sum of these two time is equal to five hours hence expressed as

`\frac {40}{x-25}+\frac {135}{x}=5\\5(x^(2)-25x)=40x+135x-3375\\5x^(2)-125x=175x-3375\\5x^(2)-300x+3375=0\\x^(2)-60x+675=0\\(x-15)(x-45)=0\\x=15 or 45`

Since speed was at a point reduced by 25, x can't be 15 hence x is 45.