Q&A - P3 Math

[CoffeeCat]

tianzhu:

help:

Please help to solve this probe.


Ali has 3 times more than Sam. After Ali lost 18 marbles and Sam bought 12 marbles, they have equal number of marbles. How many marbles did have at first?

Ali has 3 times more than Sam.

Hi

Maybe, it should be read as
Ali has 3 times more marbles than Sam.

Take note of 3 times more as compared to 3 times as many as .....

One is 4 units to 1 unit whereas the other is 3 units to 1 unit

Best wishes

This is a valid issue. I was confused by this when i was young, but from my observations of \"model answers\" in books, they treat \"3 times more than\" the same as \"3 times as many as\". Perhaps for this we really need some expert to clarify.

[P5G]

Herbie:

Thanks CoffeeCat,


I have another maths qn. Can help to solve it? Tx

Mr Tan had 1.5 litres of white paint on Tin A and 1.25litres of blue paint in Tin B. He poured 750ml of blue paint from TIn B into Tin A. He then poured some of the mixture in Tin A back into Tin B. if 7/11 of the final mixture in Tin B was made up of blue paint, what does the volume of mixture in Tin A that Mr Tan had poured into Tin B?

A -- 1500 ml White
B -- 1250 ml Blue

------------------------
1250 - 750 = 500 ml

A -- 1500 ml White + 750 ml Blue (mixture)
B -- 500 ml Blue

-----------------------
White -- 11/11 - 7/11 = 4/11 -- from A (mixture)
Blue -- 4/11 x 750/1500 = 2/11 -- from A (mixture)
7/11 - 2/11 = 5/11 -- Blue from B

5u -- 500 ml
1u -- 500/5 = 100 ml

6 u -- 100 x 6 = 600 ml paint from A (mixture)

[jesschan]

Hi! May I know is 2/1 considered to be an improper fraction?

[CoffeeCat]

jesschan:

Hi! May I know is 2/1 considered to be an improper fraction?

I guess so

[jesschan]

Thanks CoffeeCat.


Any school teachers can verify this answer? My son was given a question on fractions and the answer is 2 but it must be expressed as an improper fraction. He gave the answer as 2/1 but his teacher said it is wrong - must write as 4/2 or 6/3 etc… but he wasn’t convinced…

[jesschan]

Another question - how do you explain to a kid why a fraction divided by another fraction always gives a bigger fraction? My son can’t understand it because a whole number divided by another whole number always gives a smaller number…

[2ppaamm]

jesschan:

Another question - how do you explain to a kid why a fraction divided by another fraction always gives a bigger fraction? My son can't understand it because a whole number divided by another whole number always gives a smaller number....

Tell you something very funny. I teach maths at tertiary level, but I cannot give answers to primary school maths. Not because I don't have an answer, because I don't know what answer the teacher expects. Therefore, I cannot give the answer in case it gets your son into deeper trouble.

My son got into too many troubles because of his unique but correct answers already. Don't need another few.

Can you imagine how the kids feel, if we as adults are also afraid of right answers labelled 'wrong'? :lol:

But first, get the teacher to define 'fractions'. You will realize her definition has to be pretty sharp!

[Dharma]

jesschan:

Another question - how do you explain to a kid why a fraction divided by another fraction always gives a bigger fraction? My son can't understand it because a whole number divided by another whole number always gives a smaller number....

Hi Jesschan,

Something simple here to help him understand

1.\tIf you have a string of 3cm long and cut it to 3 equal lengths
\tEach length = 3cm/3 = 1cm

If you have string of 3cm long and you want to cut it into lengths of 1cm.
No. of lengths = 3cm / 1cm = 3

2.\tIf you have string of 3/2 cm long and you want to cut it to 6 equal lengths.
Each length = 3/2 cm / 6 = 1/4cm

If you have string of 3/2cm long and you want to cut it into lengths of 1/4cm.
No. of lengths = 3/2cm / 1/4 cm = 6






[/list]

[CoffeeCat]

jesschan:

Another question - how do you explain to a kid why a fraction divided by another fraction always gives a bigger fraction? My son can't understand it because a whole number divided by another whole number always gives a smaller number....

Must point out to your son that its the division that matters not the \"kind\".

In addition to dharma's example, you can use a fraction as a starting length, like 1/2 cm.

1/2 cm divide by 1 = 1/2
1/2 divide by 1/2 = 1

1/2 cm divide by 2 (cut in half) = 1/4
1/2 divide by 1/4 = 2.

1/2 divide by 4 = 1/8
1/2 divide by 1/8 = 4

[2ppaamm]

A slightly brighter child at P3 will ask:


What about 1/2 divide by 8/3? Does your rule still apply? or is 8/3 no longer a fraction?