Amotorboat takes 40 minutes to travel 20 miles downstream. the return trip takes 60 minutes. what is the speed of the current?

Let b be the speed of the boat, and c be the speed of the current. Then:
20/b+c=2/3 hr
20/b-c=1 hr
2/3b+2/3c=20
b-c=20
Then:
b+c=30
b-c=20
2b=50
b=25 mph
c=5 mph
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38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)