Posted by dawn on .
to save fuel on the 240 km trip to the cottage, the Nakamura family reduce their usual average speed by 20 km/h. this lengthens their journey by 1 hour. what is the slower average speed?
pleassee help! thanks :)

math  incomplete 
Ms. Sue,
How long does it usually take them to make this trip?

math 
dawn,
oh my gosh! so my teacher handed us two versions of this question...i didn't have that answer! sorry. the proper question i will repost.

math 
dawn,
never mind it does not say. does this mean the question is complete and unable to answer? its a question on an assignment and i do not know how to answer it. should ijust say uncomplete?

math 
drwls,
Let V1 = the original average speed and V2 = the slower average speed. You have these two equations in two unknowns:
V1  V2 = 20 (km/h)
240/V2  240/V1 = 1 (hour)
You want to solve for V2. Use substitution, V1 = V2 + 20
240/V2 240/(V2 +20) = 1
240*[1/V2  1/(V2+20)] = 1
20/[V2(V2+20)] = 1/240
V2*(V2+20) = 4800
You can solve this as a quadratic equation and take the positive root. You should get
V2 = 60 km/h 
math (not incomplete) 
drwls,
Note that there was enough information provided to solve for both velocities, using simultaneous equations.

math 
Anonymous,
thh

math 
Anonymous,
I LOVE MATH

math 
Rick Ross,
While this gave me the answer, I was unable to understand how this was done. 2/10 would not math again

math 
Rick Ross,
Also, shout out to my pears