math
posted by derrius .
A speedboat racer travels at a steady rate of 0.75 of a mile per 0.25 of a minute.
How many minutes does it take for the boat to travel 3 miles?
How long will it take for the boat to travel 7.5 miles?

for the first question, we just use ratio and proportion.
let x = time it takes to travel 3 miles.
0.75 mi : 0.25 min = 3 mi : x min
therefore, writing in fraction,
0.75/0.25 = 3/x
crossmultiplying,
0.75x = 0.25*3
0.75x = 0.75
x = 1 minute
for the second, we also use ratio and proportion:
let y = time it takes to travel 7.5 miles.
0.75 mi : 0.25 min = 7.5 mi : y min
thus, writing in fraction,
0.75/0.25 = 7.5/y
crossmultiplying,
0.75y = 0.25*7.5
y = 2.5 minutes
hope this helps~ :)