SOLUTION: I rode my bike 30 miles. If I had increased my average speed by 3 mph, I would have decreased my travel time by 20 minutes. How many miles per hour was my original speed? I trie

Question 684235: I rode my bike 30 miles. If I had increased my average speed by 3 mph, I would have decreased my travel time by 20 minutes. How many miles per hour was my original speed?
I tried to use d= r* t so 3x=30? I don't know what else to do
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
There are 2 equations. One is for the actual bike riding
the other is the option with higher speed.
Let = original speed in mi/hr
Let = original time in hrs
given:
(1)
(2)
( note that 20 min is 1/3 hr )
---------------------------
(2)
and
(1)
Substitute (1) into (2)
( note also that )
(2)
Subtract from both sides, then add to both sides
(2)
Multiply both sides by
(2)
(2)
Complete the square:
(2)
(2)
(2)
(2)
Take the square root of both sides ( ignore the negative square root )
(2)
(2)
(2)
Your original speed was 15 mi/hr
check:
(1)
(1)
(1)
and
(2)
(2)
(2)
(2)
(2)
(2)
OK

RELATED QUESTIONS
I rode my bike for 15 minutes. For 10 minutes I rode for 15 mph, for 5 minutes I rode... (answered by ankor@dixie-net.com)

if I rode a bike 2212 miles in 87 hours 52 minutes and 52 seconds what would my average... (answered by rfer)

If I bike 3.6 miles in 20 minutes, is my speed 18... (answered by Alan3354)

what would my speed be in MPH if I had to travel 1200 feet in 2 minutes and 20... (answered by Alan3354)

what would my speed be in MPH if I had to travel 2400 feet in 2 minutes and 20... (answered by Alan3354,josmiceli)

if I rode my bike for 14 minutes at the speed of 12 mph how far did I... (answered by checkley79)

If I rode my bike 5 miles in twenty mineuts how many mph was I... (answered by Theo)

if i rode my bike 7 1/2 miles in one hour. How far can i travel in 4.5... (answered by Alan3354)

If I rode my bike 24 mile is 70 minutes, how many miles was I riding per... (answered by Maths68)