need help Singapore 5B problem

[Lori in MS]

Please help me. I can't figure out how to do this problem.

 

 

The ratio of the number of books that Lina had to the number of books that Sulung had was 1:2. After Lina bought 24 new books, the ratio became 2:1. How many books did Lina have at first?

 

 

Thank you.

[8filltheheart]

I don't know how to solve with bar diagrams, but here is an easy explanation:

 

x= # of books Lina owns

2x= # for Sulung

 

since Lina buys 24 books, that is x+24. That is the same as now 2 times what Sulung has so that is 2(2x).

 

So....

 

x+24= 4x

24=3x

x=8

 

Does that help?

[fractalgal]

Please help me. I can't figure out how to do this problem.

 

 

The ratio of the number of books that Lina had to the number of books that Sulung had was 1:2. After Lina bought 24 new books, the ratio became 2:1. How many books did Lina have at first?

 

 

Thank you.

 

Using the bar method:

 

Here is the before case: Note: [ ] = 1 unit

 

Lina [ ]

Sulung [ ][ ] (Ratio is 1:2)

 

After Lina bought 24 new books

 

Lina [ ][ ][ ][ ]

Sulung [ ][ ] (Ratio is now 2:1)

 

So three units = 24

Then each unit = 8.

 

So Lina originally had 8 books.

Edited April 27, 2010 by fractalgal

[forty-two]

The ratio of the number of books that Lina had to the number of books that Sulung had was 1:2. After Lina bought 24 new books, the ratio became 2:1. How many books did Lina have at first?

 

L = Number of books Lina had to start with

S = Number of books Sulung had to start with

 

 

Initial (Lina's total books in blue):

[----L----][-----------S---------]

[----------][----------][----------]

 

Final (Lina's total books in blue):

[----L----][------------------+24-----------][-----------S---------]

[----------][----------][----------][----------][----------][----------]

 

To start with, Lina's initial number of books is declared to be equal to one unit of books. Since Sulung has twice as many books as Lina, Sulung therefore has two units of books.

 

When Lina receives 24 more books, the ratio of books b/w Lina and Sulung becomes 2:1. Therefore, Lina's new total amount of books is twice as much as Sulung's amount of books. Since Sulung has two units of books, Lina now has 4 units of books. Those four units are equal to one unit plus 24 books, so 24 books equals three units, and one unit equals 8 books. So Lina had 8 books to start with.

 

Does that make sense?

[Lori in MS]

Yes thank you!