SOLUTION: how do we work out how to find the answers to all these question i have tried but i get different to the answers in the book and my son is in tears.... a/ pumpa can fill a tan

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Question 731652: how do we work out how to find the answers to all these question i have tried but i get different to the answers in the book and my son is in tears....
a/
pumpa can fill a tank in 5 mins while pump b can fill a tank in 10 mins. how long will it take to fill the tank if both are working together?
b/
in making one revolution a car wheel travels 200cm . how fast are the wheels spinngin in revolutions per minute, when the car is travelling at 60km/h?
c/
a girl paddles her kayak upstream from her home to her friends home takin 2.5 hours for the journedy. sher returns taht afternoon in 1.5 hrs .
if the is flowing at 2.5 km/h find:
1/ her paddling speed in still water
2/ the distance to ther friends place.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
pump a can fill a tank in 5 mins while pump b can fill a tank in 10 mins
how long will it take to fill the tank if both are working together?
:
let m = no. of minutes required when working together
let the completed job = 1, (a full tank)
each pump does a fraction of the job. The two fractions add up to 1
m%2F5 + m%2F10 = 1
multiply by 10 to clear the denominators, resulting in:
2m + m = 10
3m = 10
m = 10/3
m = 31%2F3 min working together
:
:
b/
in making one revolution a car wheel travels 200cm.
how fast are the wheels spinning in revolutions per minute,
when the car is traveling at 60km/h?
:
Let r = number of revs at 60 km/hr (convert 60 km/h to cm/min
r = %2860%2A1000%2A100%29%2F%28200%2A60%29
r = 500 rev per minute
:
:
c/
a girl paddles her kayak upstream from her home to her friends home
taking 2.5 hours for the journey. returns that afternoon in 1.5 hrs
if the current is flowing at 2.5 km/h
find:
:
1/ her paddling speed in still water
let s = speed in still water
then
(s-2.5) = effective speed upstream
and
(s+2.5) = effective speed downstream
:
Write a distance equation; dist = time * speed
Up dist = down dist
2.5(s-2.5) = 1.5(s+2.5)
2.5s - 6.25 = 1.5s + 3.75
2.5s - 1.5s = 3.75 + 6.25
1s = 10 km/hr in still water
:
2/ the distance to the friends place.
Find the dist upstream
2.5(10-2.5) =
2.5(7.5) = 18.75 km
check using downstream equation
1.5(10+2.5) = 18.75 km also, confirms our solution
:
:
Hopefully, we can dry those tears!