Speed of the boat = u
speed of the current = v
in downstream,
u - v = 105/5
u - v = 21
in upstream
u + v = 105/7
u + v = 15
add both equations
2u = 36
u = 18
v = -3
so
speed of the boat = 18 km/h
speed of the current = 3 km/h
the ratio that is equal to 10:85 is 20:170 because if you multiply both sides by two you get 20:170
24 feet long :)
All I did was I divided the 36 into 3 equal parts of 12, then doubled the 12 to make that longer piece 24 feet. This 24 foot piece would be twice as long as the other leftover 12 foot piece since 12x2=24
X and y are books
x is fiction
y=nonifiction
x+y=36
x=12+y
12+y+y=26
2y+12=26
minus 12
2y=14
divide 2
y=7
sub
x=12+y
x=12+7
x=19
nonfiction=7
