Answer:
A. Figures with the same shape, but not necessarily the same size
Let V, be the rate in still water and let C = rate river current
If the boat is going :
upstream, its rate is V-C and if going
downstream, its rate is V+C,
But V = 5C, then
Upstream Rate: 5C - C = 4 C
Downstream rate: 5C+C = 6C
Time = distance/Rate, (or time = distance/speed) , then:
Upstream time 12/4C and
Downstream time: 12/.6C
Upstream time +downstream time:= 2h30 ' then:
12/4C + 12/.6C = 2.5 hours
3/C + 2/C = 5/2 (2.5 h = 5/2)
Reduce to same denominator :
5C = 10 and Rate of the current = 2 mi/h
After Sally had given 1/9 of her stamps to Andy, she had 280 stamps (since they now have equal shares). So 280 was 8/9 of what she started with, making the 1/9 she handed over equal to 280/8, that’s 35. And Andy was “under” by the same amount she was “over” an equal share, that’s 35 under matching her 35 over, which is 70 altogether.
By all means use algebra but you may find you can reason a word problem through in words.
