Four people want to cross the river. there is only one boat available, and it can carry a maximum of 200 pounds. the weight of the four people are 109,170,110, and 90 pounds. how can they all manage to get across the river, and what is the minimum number of crossing required for the boat?

1.  (90 + 109) →→→→  [109 stays, 90 goes back]
2.  ←←←←←←(90)← 
3. (90 + 110) →→→→   [110 stays, 90 goes back and stays there]
4. ←←←←←←(90)←   
5. (170)→→→→→→     [170 stays, 110 (оr 109) goes back]
6. ←←←←←(110)←     
7. (110+90)→→→→→  [done]

I hope this helps :)

-15 + 25 = ?

to get to zero from -15 you have to add 15 to it. you add 15 to it, by subtracting 15 from 25. 25-15 = 10

you could also just start at -15 and count forward 25 "points" to get to 10

25- 15 = 10

you could draw a number line and count back 15 from zero and from there count forward 25 and you'll get 10

Step-by-step explanation: