You know that the sum of -5 and another integer is a positive integer. What can you conclude about the sign sign of the other in
2 answers:
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Let's write some equations.
Mingwei's distance from Town A after
hours from 8:00 is 
.
Ali's distance from Town B after hours is 
, since he doesn't start walking for 40 minutes.
When Mingwei's distance is twice Ali's, they've met up (since their distance from Town A is twice their distance from Town B).
So, this gives
, so 
, so 
, so the time is 10:40.
After
hours, Mingwei has traveled 
kilometers while Ali has traveled sixty, so the distance between the towns is 
kilometers.
Mingwei's distance from Town A after
Ali's distance from Town B after
When Mingwei's distance is twice Ali's, they've met up (since their distance from Town A is twice their distance from Town B).
So, this gives
After