Question

Two trains leave the same station at the same time, but are headed in opposite directions. One train travels at 70 mph and the other train travels at 80 mph.
How much times passes until the trains are 600 mi apart?

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Answer 1

If the required difference is 600 mi, lets start of counting by 10s and multiplying the current number
800-700 = 100
1600-1400 = 200
2400-2100 = 300
3200-2800 = 400
4000-3500 = 500
4800-4200 = 600
if 60 hours pass, they will be 600 miles away from each other.
counting by 10 each time will help with problems like or similar to this.

Answer 2

Let make time = x
70x + 80x = 600
add like terms
150x = 600
isolate the x
150x / 150 = 600 / 150
x = 4

verify
4 * 70 = 280
4 * 80 = 320
280 + 320 = 600