Q&A - PSLE Math

[YumYum]

Dear MathIzzFun,


Thank you and wishing you a happy new year filled with good health n happiness.

[2DMommy]

Please help me with these questions :


1)Daniel and Kester have some pens. If Daniel gives 10 of his pens to Kester, he will have twice as many pens as Kester. If Daniel gives 6 of his pens to him, he will have thrice as many pens as Kester. How many pens does Kester have ?

2)The pages of a book are numbered 1 to 99. Find the difference between the sum of all the odd pages and the sum of all the even pages.

3)The ratio of the number of red apples to the number of green apples in a box is 4 : & . If 18 more apples are added into the box, the number of red apples will be equal to the number of green apples. How many apples are there in the box ?

Thank you !

[MathIzzzFun]

2DMommy:

Please help me with these questions :


1)Daniel and Kester have some pens. If Daniel gives 10 of his pens to Kester, he will have twice as many pens as Kester. If Daniel gives 6 of his pens to him, he will have thrice as many pens as Kester. How many pens does Kester have ?

2)The pages of a book are numbered 1 to 99. Find the difference between the sum of all the odd pages and the sum of all the even pages.

3)The ratio of the number of red apples to the number of green apples in a box is 4 : & . If 18 more apples are added into the box, the number of red apples will be equal to the number of green apples. How many apples are there in the box ?

Thank you !

Hi

1)
If Daniel gives 10 pens to Kester, Daniel's : Kester's = 2u : 1u

So, number of pens daniel has : number of pens kester has
= 2u + 10 : 1u - 10

If Daniel gives 6 pens to Kester,
Daniel : Kester
= 2u + 10 -6 : 1u -10 + 6
= 2u + 4 : 1u - 4
= 3 : 1

cross-multiply --> 2u + 4 = 3u - 12
1u = 16

Number of pens kester has --> 1u - 10 = 16 - 10 = 6

2)
1-2+3-4+5-6+7-8 ....+97-98 +99
1-2=-1
3-4=-1
5-6=-1
...
1-2+3-4+5-6...+97-98 = -49
so, 1-2+3-4+5-6+7-8 ....+97-98 +99 = 50

3) please check the question.

cheers.

[MathIzzzFun]

YumYum:

Dear MathIzzFun,


Thank you and wishing you a happy new year filled with good health n happiness.

Hi

u r welcome

Wishing you and all parents here a happy and bountiful new year !

cheers.

[anneshirleygilbert]

Hello tianzhu,


Many thanks for your quick reply. It took me a while to digest your explanation …(especially your reply to Fat Mama)… finally got it! How easy it is to misinterpret math questions!

I need a little more help on the question on vanilla and chocolate. I am able to get the answer, but my answers are derived from some cross-multipying… a little too overwhelming for my daughter. You have a fantastic way of making complex things so simple… do you mind to show your working? I shall wait patiently, seeing this is the CNY season.

Many thanks in advance.

[tianzhu]

Hi anneshirleygilbert


This is a question on “double if”. The “if” in the statement signifies the event didn’t really happen. You may solve it with UM or MD.

Actually, “cross multiply” is the same as equalising the final parts.

In “cross multiply” students need to open up or expand brackets, this is covered in Sec 1 Math.
So long as students are comfortable with expansion of brackets, they can use it.

For this slide, I’ve added in an extra table (light blue) to show the steps taken for equalisation of final parts.

Hope this helps.

Good Cheers, Good Health and a Prosperous Chinese New Year.

Best wishes

http://farm8.staticflickr.com/7007/6742265061_968d15425b_z.jpg\">

[MathIzzzFun]

anneshirleygilbert:

Hello tianzhu,


Many thanks for your quick reply. It took me a while to digest your explanation ...(especially your reply to Fat Mama).... finally got it! How easy it is to misinterpret math questions!

I need a little more help on the question on vanilla and chocolate. I am able to get the answer, but my answers are derived from some cross-multipying... a little too overwhelming for my daughter. You have a fantastic way of making complex things so simple... do you mind to show your working? I shall wait patiently, seeing this is the CNY season.

Many thanks in advance.

Hi

using MD --> http://www.flickr.com/photos/62167097@N02/6742709385/in/photostream

Wishing all a happy and bountiful dragon year !

cheers.

[anneshirleygilbert]

Thanks a million, Tianzhu!


Cross-multiplying is the same as equalizing the parts! Why didn’t I think of it thus??!! I just knew you’d throw in some light! Thank you very much!. You have a good year ahead, too!

[anneshirleygilbert]

Thank you, MathIzzzFun, for the alternate method. Appreciate your help.

[2DMommy]

Please help me with these questions :


1)There were some $5 , $10 and $50 notes in Jane’s wallet. The value of the $5, $10 and $50 was in the ratio 3 : 4 : 2. After spending 50% of her $50 notes, 10 of her $10 notes and 2/3 of her $5 notes, Jane had $200 left. Find the total amount of money Jane had in her wallet at first.

2)Some boys shared a packet of onion rings. If each boy eats 10 rings, there will be 3 rings short. If each boy takes 9 rings, there will be 4 rings extra. How many pieces of onion rings are there in the packet ?

3)Mr Singh had $315 worth of concert tickets. He sold 4 adult tickets and 3 child tickets. Each adult ticket is 1 1/2 times as much as a child ticket. If the value of the tickets Mr Singh had left is 3/7 of the original amount, what is the cost of a child ticket ?

Thank you and Happy New Year !