Tuesday

March 3, 2015

March 3, 2015

Posted by **fiona** on Thursday, April 1, 2010 at 8:43pm.

- math -
**Reiny**, Thursday, April 1, 2010 at 9:48pmlet the speed of freigh train be x mph

then speed of express is x+20 mph

time for freight to go 300 miles = 300/x

time for express to go 280 = 280/(x+20)

300/x - 280/(x+2) = 2

multiply by x(x+20)

300(x+20) - 280x = 2x(x+20)

300x + 6000 - 280x = 2x^2 + 40x

2x^2 + 20x - 6000 = 0

x^2 + 10x - 3000 = 0

(x+60)(x-50) = 0

since x > 0, x = 50

speed of freight = 50 mph

time for freight to go 300 miles = 6 hours

speed of express = 70 mph

time to go 280 miles = 4 hours

(sure enough the difference between their times is 2 hours.)

**Answer this Question**

**Related Questions**

algebra - The speed of a passenger train is 16 mph faster than the speed of a ...

algebra - the speed of a passenger train is 20mph faster than the speed of a ...

algebra - The speed of a passenger train is 18mph faster than the speed of a ...

Math - The The speed of a passenger train is 12 mph faster then the speed of a ...

algebra 1b - the speed of a passenger train is 18mph faster than the speed of a ...

MATH Algebra - The speed of a passenger train is 6 mph faster than the speed of ...

Algebra - The speed of a passenger train is 20 mph faster than the speed of a ...

problem solving - A freight train travel 53.7 miles per hour. About how many ...

math,correction - Problem #1 Number problem. If one-half of one integer is ...

math - Train A is 12 mph slower than train B. Train A travels 230 miles in the ...