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Need help with simple math problem. (lemmy.ml)

submitted 4 months ago by [email protected] to c/[email protected]

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Hi,

I found online a nice (and seemed easy) math problem.

Rocket A travel from Mars to Earth in 200 days
Rocket B travel from Earth to Mars in 150 days, but take off 30 days later

When they cross each other, which one is the closet to the earth ?

So they give a "flat" answer, without giving any explanation on how they reach this conclusion.

What would be your simplest Mathematical solution for this ?

Thanks.

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[–] [email protected] 0 points 4 months ago (1 children)

If I was explaining it to someone, I would get them to figure out the speed as a percentage of the journey.
100/200 = 0.5 per day for A
100/150 = 0.75 per day for B.

Then, I would get them to figure out where A was when B starts the journey.
30*0.5 = 15

So, we care about 85% of the journey.

What else do we know?
We know that the ships get 1.25% of the total distance each day if they are leaving from opposite sides (0.5 + 0.75).

So, that turns this into the question "How many days does it take to go 85 if you are going 1.25 per day? (85/1.25)"

[–] [email protected] 0 points 4 months ago

Not a bad approach, but 100/150 is 0.6666, not 0.75.