Question 898281
At 10:30am two planes leave Houston, one flying east at 560 km/h and the other west at 640 km/h. At what time will they be 2100 km apart?

I'm not sure what formula to put this in to solve it. I believe the answer is 1 hr 45 min travel time so it would be 12:15pm. I know RxT=D, but how do I incorporate these in that formula. I'm confused.

I drew a picture and added the 2 rates together, so in 1 hr they are 1200 km apart. Then I added 30 min, so half of 1200 is 600 which would equal 1800 km. Then I added 15 min which would be half of 600 is 300. So 1200(1 hr) + 600(30 min) + 300(15 min) = 2100 km (1 hr 45 min). 10:30am + 1 hr 45min= 12:15pm
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At the time they are 2,100 km apart, both would have traveled distances that sum to 2,100 km
Let time it takes for them to be 2,100 km apart, be T
Thus, we have: 560T + 640T = 2,100
1,200T = 2,100
T, or time taken for both to be 2,100 km apart = {{{2100/1200}}}, or {{{1.75}}} hours, or 1 hour, 45 minutes after 10:30 am,
which is: {{{highlight_green(12:15 pm)}}}
That makes you CORRECT, but you could've made the solution a lot easier.