Given: d = rt, where "d" is distance, "r" is rate, and "t" is time.
One car leaves point A and travels due north at 50 mi/hr. Another
car leaves point A 3 hours later and travels due south at 70 mi/hr. When
will the two cars
be 1,000 miles apart?

Question

Given: d = rt, where "d" is distance, "r" is rate, and "t" is time.
    One car leaves point A and travels due north at 50 mi/hr. Another
    car leaves point A 3 hours later and travels due south at 70 mi/hr. When
    will the two cars
    be 1,000 miles apart?

phi · Answer

the easiest way to do this problem is to know that the cars are moving apart at a rate of
50+70  = 120 miles/hour

deathslasher99 · Answer

ok

welshfella · Answer

yes  -  i used a different method and got a bit tied up!!!

phi · Answer

except for the first 3 hours, when only one car is moving at 50 mph
in 3 hours it goes 150 miles

1000- 150 = 850 miles
are left to go, at a rate of 120 mph

deathslasher99 · Answer

im following
but whats with the 120?

phi · Answer

if one car is moving north at 50 mph
and the other car is moving south at 70 mph
they are moving away from each other at (50+70)= 120 mph

deathslasher99 · Answer

oh ok

phi · Answer

in other words, assuming they started at the same time ,
they would be 120 apart after 1 hour
240 miles in 2 hours
or in general   rate *time  = 120 * # of hours.

deathslasher99 · Answer

so the anwser counts as 120 mph

deathslasher99 · Answer

??

phi · Answer

When will the two cars be 1,000 miles apart?

you have to think it  out a bit.
for 3 hours , only 1 car is moving (north at 50 mph)
so in 3 hours, the two cars are 150 miles apart.
we want a total of 1000 miles, so they have to move another 850 miles
and after 3 hours both cars are moving at a combined rate of 120 mph
so we need the time it takes for them to go 850 miles
then add the first 3 hours  to get the total time.

how long does it take to go 850 miles at rate= 120 mph ?

deathslasher99 · Answer

around 7 hours, correct?

phi · Answer

7 and 1/12 hours

or 7 hours  5 minutes

now add the first 3 hours when only 1 car was moving

the cars will be 1000 miles apart
10 hours 5 minutes
after the first car started.

phi · Answer

and 7 hours 5 minutes after the 2nd car started.

phi · Answer

The question is a bit vague about how to specify the time.

deathslasher99 · Answer

yes

phi · Answer

if they told us the first car left at noon, then we could say the two cars are 1000 miles apart at 10:05 pm

deathslasher99 · Answer

so they where asking for the total thoe correct which is 10 hr 5m

phi · Answer

the question is not clear.  I would answer the "when" by saying
10 hr 5 min after the first car started

deathslasher99 · Answer

oh

phi · Answer

any questions ?

deathslasher99 · Answer

nope, thank you