Q&A - P3 Math

[usaik]

wenray:

2. A big ball has a mass of 8kg and a small ball has a mass of 4kg. The total number of big and small balls is 56 and their total mass is 280kg.
a) How many big balls are there?
b) How many small balls are there?

At P3, for this kind of question i think it may be easier for a child to answer via guess and check method. Just draw a table, divide 56 into half and start guessing & checking.
http://i56.tinypic.com/2dl9abn.jpg\">

[tianzhu]

wenray:

2. A big ball has a mass of 8kg and a small ball has a mass of 4kg. The total number of big and small balls is 56 and their total mass is 280kg.
a) How many big balls are there?
b) How many small balls are there?

Hi

This question is similar to those such as “Counting Heads and Legs” types.
P4 students should be familiar with questions like this one.

Lincoln visited a farm where he saw some cows and ducks. There were 75 of them. He then counted the legs of the animals and found that there were 220. How many animals of each type were there in the farm?

A common method to solve it is using a heuristics known as “ Making a Supposition” or “Assumption Method”

Assume that all the balls are of the small types, that is a mass of 4kg.

56x4 ------ 224
280 – 224 ------ 56

8 - 4 --------- 4

Number of big balls ------- 56/4 ------- 14
Number of small balls ------- 56 – 14 ------- 42

Best wishes

[wenray]

thanks all for your help!

[tianzhu]

cwc:

Hi Tianzhu,
Very curious, what do you use to produce all these fantastic diagrams/pics to explain?
Impressive :salute: How much time do you need to typically come up with one?

Hi cwc

Good Morning.

I am happy you liked my “masak masak” way of doing maths.

Just like any solutions in this forum, you’re correct to say that efforts are put in to post them.

I am a simple daddy, so I am not very conversant with IT. At times I need to play around with the software which I used in my solutions, which is PowerPoint in this case.

The usual process starts with coming up with some thoughts on the mathematical solutions to the questions. The thoughts are then translated into usually pictorial presentation which I hope will help students see that Maths is beautiful.

Best wishes

[tianzhu]

mama_10:

hi tianzhu, thks !

:salute:

Hi mama_10

Good Morning.

You're welcome.

Best wishes

[tianzhu]

usaik:

This is a P4 question.


Draw a straight line through the point D. Then, construct another line perpendicular to the line that you have drawn and it has to cut through point E.

Below is the child's answer. My question is the second line touches point E and it crosses the straight line through point D. Would this answer be take as correct or incorrect?
http://i55.tinypic.com/11c5gu1.jpg\">

Hi

The answer is correct.
Mark a right angle to show perpendicular lines.

Best wishes

[Champion]

Hi All,

Greetings! Need helps with the following 2 questions from DD1's school past year exam papers. TIA!

1) There were 20 questions in an IQ quiz. All the questions must be answered. 3 marks were awarded for any correct answer and 1 mark was deducted for any wrong answer. If Joseph scored 48 marks, how many questions did he answer correctly?


2) Mrs. Tay has a bag of sweets. If she gives each child 7 sweets, she will be left with 5 sweets. If she gives each child 9 sweets, she will need 5 more sweets.
a) How many children are there?
b) How many sweets are there?

:thankyou:

[tianzhu]

Hi


For Q1, you may use a heuristics known as “Make a Supposition”

For every wrong question, he lost (3+1) or 4 marks.

Assume or pretend that Joseph answer 20 questions correctly

20 x 3 ------- 60
60 – 48 ------ 12

Number of wrong questions ------- 12/4 ------- 3
Number of correct answers --------20 – 3 ------17

http://farm6.static.flickr.com/5107/5682971233_63f45f06ba_z.jpg\">

The second question touches on “Gap and Difference”

Look at this question from another angle, if Mrs Tay gives 2 more sweets (9-7) to her children, she would need (5+5) or 10 more sweets.

10/2 ------ 5
There are 5 children.

Number of sweets ------ (5*7) + 5 ------ 47 or (5*9) – 5 ------- 40

Best wishes

http://farm6.static.flickr.com/5063/5683393848_c80b1a22d7_z.jpg\">

[Thein]

Hi Tianzhu


I need a help.

First, I should thank you for I was able to understand model drawing only with your explanations. Thanks a lot.

i’ve taught my child, model drawing to solve problems like :
Mrs. Tay has a bag of sweets. If she gives each child 7 sweets, she will be left with 5 sweets. If she gives each child 9 sweets, she will need 5 more sweets.
a) How many children are there?
b) How many sweets are there?

but for this problem:

Mrs. Raju bought a sack of rice which weighed less than 50kg. If she packed the rice into bags of 5kg each, she would have 3kg of rice left. If she packed it into bags of 7kg each, she would have 4kg of rice left. How many kg of rice did Mrs. Raju buy?

i couldn’t draw the model.

i’ve to go for another heuristic approach. finding the multiples…

i don’t know how to differentiate the problems…or is there any common method that i can teach my kid…

Thank you in advance.

[corneyAmber]

Thein:

Mrs. Raju bought a sack of rice which weighed less than 50kg. If she packed the rice into bags of 5kg each, she would have 3kg of rice left. If she packed it into bags of 7kg each, she would have 4kg of rice left. How many kg of rice did Mrs. Raju buy?

Here is a possible solution:
For this question, you can apply Guess and Check method as 50kg is given as the upper limit, a table can be drawn.

7X6 = 42+4 = 46 => packed into 5, R=1
7x5 = 35+4 = 39 => packed into 5, R=4
7x4 = 28+4 = 32 => R = 2
:
:
7x2 = 14+4 = 18 => R=3

So answer is 18kg.