Q&A - P3 Math

[tianzhu]

Hi, young man muffins


May you have a wonderful time in your secondary school. Enjoy your studies and CCA.

Good cheers, Good health and a Happy New Year.

I’ve not been posting solutions actively because I am getting rusty as I’ve not been reading up much since PSLE. Also, kiasu PSLE 2010 kids are very fortunate to have a professional tutor like mathsguru who is pretty keen in offering her expertise in the self help threads.

Best wishes

[Muffins]

Oh... But besides Maths, we love talking to you, please login more! :please:

[belladona]

tianzhu:

Hi

Hope this helps.

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Best wishes

Yes, thanks........

[fanren]

Hi

i have a qn hope someone can help.

Bobby places 12 cards on a table. Each card is either red or black in colour. If the fraction of black cards is 7/12, what is the smallest number of additionals cards that Bobby needs to put on the table so that the fraction of black cards becomes 5/8 ?

thanks in advance!

[BigDevil]

fanren:

Hi

i have a qn hope someone can help.

Bobby places 12 cards on a table. Each card is either red or black in colour. If the fraction of black cards is 7/12, what is the smallest number of additionals cards that Bobby needs to put on the table so that the fraction of black cards becomes 5/8 ?

thanks in advance!

Not sure if my understanding is correct...

7/12 = 14/24
5/8 = 15/24

So Bobby needs to put 1 additional card?

[fanren]

BigDevil:

fanren:

Hi

i have a qn hope someone can help.

Bobby places 12 cards on a table. Each card is either red or black in colour. If the fraction of black cards is 7/12, what is the smallest number of additionals cards that Bobby needs to put on the table so that the fraction of black cards becomes 5/8 ?

thanks in advance!

Not sure if my understanding is correct...

7/12 = 14/24
5/8 = 15/24

So Bobby needs to put 1 additional card?

the answer is 4 cards, i am thinking is it 5/8 = 10/16, so 12 + 4 = 16 ? hope someone who knows can help and share. thanks

thanks BigDevil for trying !

[Dharma]

fanren:

BigDevil:

[quote=\"fanren\"]Hi

i have a qn hope someone can help.

Bobby places 12 cards on a table. Each card is either red or black in colour. If the fraction of black cards is 7/12, what is the smallest number of additionals cards that Bobby needs to put on the table so that the fraction of black cards becomes 5/8 ?

thanks in advance!

Not sure if my understanding is correct...

7/12 = 14/24
5/8 = 15/24

So Bobby needs to put 1 additional card?

the answer is 4 cards, i am thinking is it 5/8 = 10/16, so 12 + 4 = 16 ? hope someone who knows can help and share. thanks

thanks BigDevil for trying ![/quote]Hope this helps

At first
Black : 7
Red : 5

If B number of black cars added and R number of red cards added

Black : 7 + B
Red : 5 + R
Total no. of cards = 12 + B + R

Fraction of black cards = 7 + B/ (12 + B + R) = 5/8
Fraction of red cards = 5 + R/ (12 + B + R) = 3/8

8(7+B) = 5(12 + B + R)
56 + 8B = 60 + 5B + 5R
3B = 5R + 4

Smallest no. of cards added is by adding 1 red card ; and 3 black cards
3B = 5(1) + 4
B = 9/3 = 3
B + R = 3 + 1 = 4

New fraction of black cards = 7 + 3/ (12 + 3 + 1) = 10/16 = 5/8

[BigDevil]

:faint:

[fanren]

Thanks a million for your answer plus explanation, Dharma!!!

[P5G]

fanren:

Hi

i have a qn hope someone can help.

Bobby places 12 cards on a table. Each card is either red or black in colour. If the fraction of black cards is 7/12, what is the smallest number of additional cards that Bobby needs to put on the table so that the fraction of black cards becomes 5/8 ?

thanks in advance!

Sorry for the blunder. Below are my corrections.

5/8 x 2/2 = 10/16

16 - 12 = 4 additional cards