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 By: Tping (offline)  Monday, March 25 2013 @ 07:22 PM CDT (Read 1327 times)
Tping

At Station A, the ratio of the number of children to the number of adults on a train was 4:5.
At the next station, 12 children alighted and 10 adults boarded the train.
The ratio of the number of children to the number of adults on the train then became 7:10.
How many children were on the train at first?

Thank you.

Junior

Registered: 01/26/12
Posts: 25

 By: angeliakwok (offline)  Friday, March 29 2013 @ 08:22 PM CDT
angeliakwok

This concept is usually called external change, as the change values changes the end ratio units.
LCM the end ratio units to create an equal stage, as you would in simultaneous change

(C4u - 12 = 7p) x 10
(A5u + 10 = 10p) x 7

C40u - 120 = 70p
A35u + 70 = 70p

therefore

5u is 120 + 70 = 190
1u is 38

Children at first is 4 x 38 = 152

apologies I draw models but i dont how to do it with this app

Newbie

Registered: 02/17/11
Posts: 5

 By: T0116060A (offline)  Saturday, August 10 2013 @ 11:36 PM CDT
T0116060A

This sum is actually (EVERYTHING CHANGES)
Now, do you know how to do this sum?
If you don't know how to do this sum, please clarify with me or Edward.....
Thank you!

Newbie

Registered: 08/10/13
Posts: 10

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