Tutor MathsGuru: Ask me for your burning Maths questions!

[maths6a]

super star:

hi

I went through the problem & the working .but still cannot understand that.please explain this problem

maths6a:

[quote=\"beauty queen\"]Please help me with this question,

There are some black and white marbles in a bag. If 20 black marbles are removed from the bag, the total number of marbles left will be 7 times the number of black marbles left. If 50 white marbles are removed from the bag, the total number of marbles left will be 5 times the number of black marbles left. How many marbles are there in the bag.

Using algebra which in this case is cross multiplication:
When you remove 20 black marbles, the ratio of total marbles left to black marbles left is 7 : 1 so
white to black will be 6 : 1.
so number of white to black at first will be
6 units : 1 unit + 20
then question says to remove 50 white marbles are from the bag so
whilte --- 6 units - 50 ------- 4 equation 1
black ---- 1 unit + 20 -------1 equation 2
multplying equation 2 by 4 because the LCM of 1 and 4 is 4,
equation 2 becomes 4 units + 80
so now 6 units - 50 ---- 4 units + 80
2 units = 80 + 50 = 130
1 unit = 65
number of marbles in the bag = 7 units + 20
= 475
Hope this method is easier for you?






http://www.postimage.org/image.php?v=aVmQl6J
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[Cheerfuldad]

Hi all,


Please help!

Q1. Kailing and Jim had a total of $63. Kailing gave 0.3 of her share to Jim. Jim then gave 1/3 of the total amount of money he had to his brother. In the end, all the three children had the same amount of money. How much money did Kailing have at first?

Q2. A stack of bookmarks was shared among Peter, Tom and Jerry. Peter received 3 more than 50% of the bookmarks. Tom received 5 more than half of the remaining bookmarks. After Peter and Tom had taken their share. Jerry received 50% of the remainder and the last 3 bookmarks. What percentage of the stack of bookmarks did Jerry receive?

Q3. A dressmaker had some buttons. She used 1/7 of them on Monday and 1/11 of the remainder on Tuesday. On Wednesday, she bought 255 buttons and then had as many buttons as she had at first. How many buttons did she have at first?

Q4. A group of boys played only two types of sport during recess. 1/4 of them played badminton and 2/3 of them played football. 1/6 of the boys played both sports and 90 boys did not play any sports at all. How many boys were there?

TIA!

[Vanilla Cake]

Cheerfuldad:

Q1. Kailing and Jim had a total of $63. Kailing gave 0.3 of her share to Jim. Jim then gave 1/3 of the total amount of money he had to his brother. In the end, all the three children had the same amount of money. How much money did Kailing have at first?

Refer to http://www.onsponge.com/forum/35-thinkingmathonsponge/4321-p5-working-backwards.html.
This is a 5-mark question from Nanyang Primary School 2009 P5 CA2 paper 2 Q18.

Cheerfuldad:

Q2. A stack of bookmarks was shared among Peter, Tom and Jerry. Peter received 3 more than 50% of the bookmarks. Tom received 5 more than half of the remaining bookmarks. After Peter and Tom had taken their share. Jerry received 50% of the remainder and the last 3 bookmarks. What percentage of the stack of bookmarks did Jerry receive?

Refer to http://www.onsponge.com/forum/35-thinkingmathonsponge/4310-pr-5-remainder-concept.html#4325.
This is a 5-mark question from Nanyang Primary School 2009 P5 CA2 paper 2 Q17.

Cheerfuldad:

Q3. A dressmaker had some buttons. She used 1/7 of them on Monday and 1/11 of the remainder on Tuesday. On Wednesday, she bought 255 buttons and then had as many buttons as she had at first. How many buttons did she have at first?

6/7x10/11=60/77
17/77-> 255
77/77 -> 1155
Number of buttons that the dressmaker had at first = 1155.

This is a 4-mark question from Nanyang Primary School 2009 P5 CA2 paper 2 Q13.

Cheerfuldad:

Q4. A group of boys played only two types of sport during recess. 1/4 of them played badminton and 2/3 of them played football. 1/6 of the boys played both sports and 90 boys did not play any sports at all. How many boys were there?

1/4-1/6=1/12
2/3-1/6=1/2
1-1/12-1/2-1/6=1/4

1/4->90
4/4-> 90x4=360
Number of boys = 360

This is a 3-mark question from Nanyang Primary School 2009 P5 CA2 paper 2 Q6.

For the benefits of readers in this forum, it's good if you are able to state the source of your questions and given answers if available.This will help to save time for potential problem solvers rendering their help to your questions.
Thanks.

VC's mum

[tiger262]

tianzhu:

Hi


Hope this helps.
The drawing is not drawn to scale.

Best wishes
http://farm5.static.flickr.com/4116/4944993552_7c6bcaebd8_z.jpg\">

Hi Dharma,

This is regarding the question about 4-cm cubes being cut out of a wooden block, leaving behind a 'L-shaped' wooden block.

Tianzhu has kindly provided a neat diagram with dimensions for the L-shaped block. Can you please provide the solution for calculating the total surface area of the left-over L-shaped block? Please help.

Thanks a lot.

[tianzhu]

Hi tiger262


The surface area is the sum of all the areas of all the shapes that cover the surface of the L shaped block.

Find the surface area of the original block (473824), then minus (3644)2.
Use the formula, Area=LengthBreadth, you should be able to arrive at an answer of 4484sqcm.

Try it out.

Best wishes

[Dharma]

tiger262:

tianzhu:

Hi


Hope this helps.
The drawing is not drawn to scale.

Best wishes
http://farm5.static.flickr.com/4116/4944993552_7c6bcaebd8_z.jpg\">

Hi Dharma,

This is regarding the question about 4-cm cubes being cut out of a wooden block, leaving behind a 'L-shaped' wooden block.

Tianzhu has kindly provided a neat diagram with dimensions for the L-shaped block. Can you please provide the solution for calculating the total surface area of the left-over L-shaped block? Please help.

Thanks a lot.

Hi tiger262,

Total surface area of left-over block
= 2[(36 x 3) + (47 x 2)]cm2 + 2[47 x 24]cm2 + 2[38 x 24]cm2
= [404 + 2256 + 1824]cm2
= 4484cm2

I was thinking if 2 cuts of 36cm length spaced at 44cm are made perpendicular to the side of 47cm length leaving 1.5cm on either side. Then cut off the 44cm x 36cm x 24cm block from the original block and we are left with a U shaped block.

Really need Tianzhu’s help me on the illustration so that we can visualize better. This may gives a different total area.

[tiger262]

Hi Dharma and Tianzhu,


Thank you very much for your quick solutions.
Sincerely speaking, through this forum, you both are helping more students in Maths than any tutor does or can. Of course both of you will humbly under-state the value of your service. But the students are truly grateful to you for your help.

Thanks and Regards.

[Dharma]

tiger262:

Hi Dharma and Tianzhu,


Thank you very much for your quick solutions.
Sincerely speaking, through this forum, you both are helping more students in Maths than any tutor does or can. Of course both of you will humbly under-state the value of your service. But the students are truly grateful to you for your help.

Thanks and Regards.

For me the greatest satisfaction is when a child is able to learn something new from our discussions here and find our input beneficial to them. There are some out there who come from very humble background and may not able to afford tuition even if they have difficulties with maths. This is a small way of giving back to society.

[Hifive]

Hi all,


Need help with this question (source: P5 - Nanyang Pri Sch CA2):

The ratio of Ahmad’s age to Suri’s age is 5:3 now. 4 years ago, the ratio was 7:4. How old is Ahmad now?

Thanks in advance!

[Dharma]

Hifive:

Hi all,


Need help with this question (source: P5 - Nanyang Pri Sch CA2):

The ratio of Ahmad's age to Suri's age is 5:3 now. 4 years ago, the ratio was 7:4. How old is Ahmad now?

Thanks in advance!

Now
Ahmad : Suri = 5 : 3

4 years ago
Ahmad : Suri = 7 : 4

Difference in age = 2u = 3p

5u = 5 x 1.5p = 7.5p
7.5p – 7p = 4
1p = 8
1u = 8 x 3/2 = 12
Ahmad’s age now = 5u = 5 x 12 = 60