Q&A - P3 Math

[jon00]

Ann and Betty had the same number of bookmarks.

After Ann had given away 120 bookmarks, Betty had 4 times as many bookmarks as Ann.
How many bookmarks did both of them have at first?
How to draw the model to get the answer?
Thanks in advance.

[tpybear]

jon00:

Ann and Betty had the same number of bookmarks.

After Ann had given away 120 bookmarks, Betty had 4 times as many bookmarks as Ann.
How many bookmarks did both of them have at first?
How to draw the model to get the answer?
Thanks in advance.

Happy New Year! First thing to note for this kind of problem sum is The number of bookmarks for Betty remained unchanged. We need to use the before and after approach for this sum.

BEFORE
A [__________]
B [__________]
AFTER
A [_]<--120-->
B [_][_][_][_]

Since both of them have equal number of bookmarks at first,
3u-> 120
1u-> 120/3=40
Ann has 40+120=160
Total = 160*2= 320(done)

[jon00]

Happy New Year!

Thanks tpybear for your answer. The answer sheet gave an answer of 400 which confused me though.

tpybear:

jon00:

Ann and Betty had the same number of bookmarks.
After Ann had given away 120 bookmarks, Betty had 4 times as many bookmarks as Ann.
How many bookmarks did both of them have at first?
How to draw the model to get the answer?
Thanks in advance.

Happy New Year! First thing to note for this kind of problem sum is The number of bookmarks for Betty remained unchanged. We need to use the before and after approach for this sum.

BEFORE
A [__________]
B [__________]
AFTER
A [_]<--120-->
B [_][_][_][_]

Since both of them have equal number of bookmarks at first,
3u-> 120
1u-> 120/3=40
Ann has 40+120=160
Total = 160*2= 320(done)

[TwoChildren]

Hi,


BEFORE
A [______x______]
B [______x______]

AFTER
A [__x - 120__]
B [____________x + 120____]

A = x - 120
B = 4A = x + 120

4 * (x - 120) = x + 120
4x - 480 = x + 120
4x - x = 480 + 120
3x = 600
x = 200

Thus A + B = 2x = 2 * 200 = 400

I'm not from Singapore. When I did study ages ago (I'm old now, got my son in P3 this year), my teacher told me different approach on solving this. I don't know in Singapore whether it is allowed to use other approach as long as the result is correct. Anyway, I would like to share with you the other approach.

A = x - 120
B = 4A = x + 120

x + 120 = 4A
x - 120 = A
----------------- - ===> Substract to remove x, thus only 1 variable left
240 = 3A
A = 80
B = 4A = 4 * 80 = 320
A + B = 80 + 320 = 400

I hope my explanation helps

[lect]

Hi, may i know how to solve this problem sum - John’s mass is half of his own mass plus 30kg. what is his mass?

Thank you.

[tianzhu]

lect:

Hi, may i know how to solve this problem sum - John's mass is half of his own mass plus 30kg. what is his mass?

Thank you.

Hi

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8095/8381875925_c14ea89891_z.jpg\">

[ChiefKiasu]

tianzhu:

lect:

Hi, may i know how to solve this problem sum - John's mass is half of his own mass plus 30kg. what is his mass?

Thank you.

Hi

Hope this helps.

Best wishes ...

Thanks Tianzhu! Clear as a crystal as usual.

[hercules]

jon00:

Ann and Betty had the same number of bookmarks.

After Ann had given away 120 bookmarks, Betty had 4 times as many bookmarks as Ann.
How many bookmarks did both of them have at first?
How to draw the model to get the answer?
Thanks in advance.

http://i50.tinypic.com/xe337l.png\">

[BigDevil]

jon00:

Ann and Betty had the same number of bookmarks.

After Ann had given away 120 bookmarks, Betty had 4 times as many bookmarks as Ann.
How many bookmarks did both of them have at first?
How to draw the model to get the answer?
Thanks in advance.

We have seen answers of 320, as well as 400.
The key to the different answers is that some assume the bookmarks were
given to Betty (400), while some don't (320).
The question said \"Ann had given away 120 bookmarks\", but it didn't say they were given to Betty.

So, I tend to agree with the 320 answer, ie. the 120 bookmarks were given to someone else.

[hercules]

tracywham:

Hi, sorry to trouble all of you again and need your help to solve this question.


Dave has 11 times as much as Oscar. Calvin and Dave have $172. Calvin and Oscar have $92. How much does Calvin have?

Solving for fun (below is the way I train my own kids).

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