Q&A - P3 Math

[SAHM Chew]

ericleets:

Hi, need help below.

John bought total 22 pens and pencils.
Each pencil cost $1 and each pen cost $1.50
He spent total $27.
How many pens and pencils did he buy?

It was told that can only use assumption than guess and check method.
My working below.

Assume 22 pencils; 22x$1=$22;
$27-$22=$5;
$5÷$1=5
But 5pens is $7.50?

I am stuck here. Please help.

Thanks

Assume 22 pencils $22 x $1 =$22
$27 - $22 = $5
$5 / $0.50 = 10 pens
22 - 10 = 12 pencils.

[ericleets]

Many thanks for your explanation…

Have a great day.

[ericleets]

Hi Parents,


Need help again.

John bought a total of 50 roses and sunflowers.
Each rose costs $3 and each sunflower costs $1 less.
She spent a total of $120.
How many roses and sunflowers did she buy?

Thanks in advance.
Eric

[BigDevil]

:yikes: Still working on Math problems 4 days before Christmas??


Rose $3; Sunflower $2

Assume all sunflowers: 50 x $2 = $100
Difference: $120 - $100 = $20
Divide: $20 / $1 = 20

20 roses, 30 sunflowers.

Check:
(20 x $3) + (30 x $2) = $60 + $60 = $120

[qms]

BigDevil:

:yikes: Still working on Math problems 4 days before Christmas??

http://i875.photobucket.com/albums/ab313/Burzuk2/Emoticons/smiley/ybs-28.gif\">

And you are still solving Math problems 4 days before Christmas?

[BigDevil]

Kekeke...good service mah.

[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