given: first part of trip x/50, second part (D-x)/60, find x/50-?
st(1) x/50 +(D-x)/60=10 and D=530, Sufficient as we can find x=350 and 350/50=7
st(2) x/50=(D-x)/60 + 4 Not Sufficient as we are missing data/parameters here to solve one equation with two variables

IOM A

You can see why the second clue doesn't work if you check for two very different values for the "remaining" distance. If the remaining distance is 6 inches, it took a second or so less than 4 hours to drive the fifty miles. If the remaining distance is 60 miles, it took 5 hours to drive the first x miles.

Gr8 Solution. Off lately i have started understanding your complexities.

Night reader wrote:given: first part of trip x/50, second part (D-x)/60, find x/50-?
st(1) x/50 +(D-x)/60=10 and D=530, Sufficient as we can find x=350 and 350/50=7
st(2) x/50=(D-x)/60 + 4 Not Sufficient as we are missing data/parameters here to solve one equation with two variables

IOM A

ithamarsorek wrote:

Julio drove for x/50 hours to cover his first x miles. He drove the remaining distance at an average rate of 60 miles per hour. We want x.

(1) This tells that Julio drove the remaining 530 - x miles in 10 - (x/50) hours, such that (530 - x)/ [10 - (x/50)] = 60; [spoiler]x can be solved uniquely. Sufficient[/spoiler]

(2) We don't know the total distance Julio drove, if it's d then

x/50 = 4 + {(d - x)/60}, this is one equation with two variables, [spoiler]no unique x can be found out of it. Insufficient



A[/spoiler]