Q&A - P3 Math

[tianzhu]

concerned1970:

Gd afternoon, it is P3 ques. Tysm for yr generous help. I know the ans to all ques but my son still doesn't get it when I tried to explain it to him. That's why I need yr help with yr models. So sry to trouble u.

Hi concerned1970

You're welcome.

It’s important to know that MD is one of many heuristics in the primary maths syllabus. Besides MD, it’s good to consider other problem solving strategies as it offers students greater versatility in problem solving.

A student with a wider range of strategies is better able to adapt to challenges when he/she faces unfamiliar questions in examinations. Just like football, a team is able to change shape when dealing with different opponents.

A bill of $72 was paid with $10, $5 and $1 notes, if 13 notes were used for payments, how many notes of each kind were used?

For this question, it helps if a student is well versed in number bonds.

A little bit of planning helps to avoid unnecessary guesses.

The bill of 72 has a number bond of 60 and 12.
12 ------ 10+2 or 10+1+1 or 5+5+1+1, we are using 2 because we are dealing with multiples of $5 and $10.

So we need 2 $1 note, leaving a difference of $70 (72- 2 -----70)

You may start with GC or Listing

Set up a tabulated list with $10, $5 and $1 as headings.

Make calculated guesses to get a number of $10 and $5 notes (total number of 11 with a value of $70).

It shouldn’t be too tedious to arrive at 3 $10 notes and 8 $5 notes.

(3*10) ----- 30
(8*5) ----- 40
(2*1) ------ 2

Therefore we have 3 $10 notes, 8 $5 notes and 2 $1 notes.

Try out the other two questions, if you need any help, please let me know.

Best wishes

[concerned1970]

Hi Tianzhu, I got different ans for ques 3 (dollar notes). 3 $10, 8 $5 and 2 $1. Is there any other method to work out this pb sum besides guess and check method? I duno how to draw models for ques 2 and 5. Can you help me with the models drawings? Ty.

[teh_oh]

concerned1970:

5) Mr Li bought 100 fish for $100. He paid $3 for each big fish and $1 for 3 small fish. How many big fish and how many small fish did Mr Li buy?

Hi,
Is the answer
25 Big Fish and 75 Small Fish?

(while i still scratching my head, my child gave me this answer.......but he said he use trial and error. :oops:)

[tianzhu]

concerned1970:

Hi Tianzhu, I got different ans for ques 3 (dollar notes). 3 $10, 8 $5 and 2 $1. Is there any other method to work out this pb sum besides guess and check method? I duno how to draw models for ques 2 and 5. Can you help me with the models drawings? Ty.

Hi concerned1970

I am sorry.I misread it as $2 notes instead of $1 notes.

I'll revise the solution.

I am sorry for the inconvenience.

For Q3, GC or Listing is quite appropriate for P3 students.It takes a little of planning and logical thinking, and it's not too tedious to arrive at the solution.

For Q2 and Q5, GC or TE is also suitable at P3 level.Again the numbers are not too big, so it is not too tedious to make calculated guesses.

I don't think MD is appropriate for Q2 and Q5.
However, \"Make a Supposition\" is a more efficient method to solve such questions.It is usually used by pupils in upper primary.

I'll try to do them tomorrow.

Best wishes

[tianzhu]

teh_oh:

Is the answer
25 Big Fish and 75 Small Fish?
(while i still scratching my head, my child gave me this answer.......but he said he use trial and error. :oops:)

Hi

Your answers are correct.

Best wishes

[teh_oh]

tianzhu:

teh_oh:

Is the answer
25 Big Fish and 75 Small Fish?
(while i still scratching my head, my child gave me this answer.......but he said he use trial and error. :oops:)

Hi

Your answers are correct.

Best wishes

Hi Tianzhu,

Thanks! Anyone can post the workings? My child solved it using trial and error.

Looking forward....

[tianzhu]

teh_oh:

Hi Tianzhu,


Thanks! Anyone can post the workings? My child solved it using trial and error.

Looking forward....

Hi teh_oh and concerned1970

A quick one first using “Make a Supposition”. I’ll try to put up the solution in tabulated form using PowerPoint at a later time if there is a need.

Suppose there were 100 big fish.

We have 100B ----- $300 (100B ---- 100 big fish, and 100*3 ------$300)

Consider a group of 3 small fish @ $1

97B and 3S ------- $292 (97 big fish and 3 small fish ----- 292)

300 – 292 ------8

So, every increase of 1 group of 3 small fish will lead to a drop of $8.

300 – 100 -----200
200/8 ------25

We have 25 groups of 3 small fish, which is 75 small fish.

Hence we have 25B and 75S.

Best wishes

[teh_oh]

Thanks Tianzhu.


Can't believe this is the standard P3 questions nowadays.

[tianzhu]

Hi concerned1970


Good Morning

Here's the solution for your \"mangoes and oranges\" question in diagram.

I've drawn picture of mangoes and oranges in my solution, but in examination, a student may draw circles and squares or circles in different colours for the representation. You don't need to draw perfect circles or squares, just some neat diagrams will do.

As usual, I’ve shown more diagrams to show the flow of events. Once you are able to see the logic behind the solution, you may reduce the number of diagrams or solve this question without MD in the future.

Hope this helps.

Best wishes

http://farm6.static.flickr.com/5140/5536110666_92946a6e2a_z.jpg\">

[tianzhu]

teh_oh:

Thanks Tianzhu.


Can't believe this is the standard P3 questions nowadays.

Hi teh_oh

Good Morning.

Such questions are common in P3 and P4. I remember seeing them a few years ago when my boy was in P3/P4.

This question is a variation from the usual” Counting heads and legs” questions.

Q1) Xie Ming Ming has 6 chickens and cows in a farm. There are 16 legs altogether. How many cows are there?

Q2) Masha 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?

For the \"Big and small fish question\", you need to increase/decrease in groups of three.

For lower primary, it’s appropriate to use GC with calculated guesses as the numbers are usually not too big.

I remember my boy started from drawing simple diagrams like circles with two or four lines to represent legs, GC and then moving to “Make a Supposition” to solve such questions.

This solution is for a P6 question, you may apply the same logic to solve the \"Big and small fish question\"as well. You’ll get the right combination at the first try.

http://farm6.static.flickr.com/5052/5456348000_75a99120c9_z.jpg\">

Here’s another two similar type of questions.

Q1) Jia Ling paid $25 for 35 pens and pencils altogether. The pens were sold at $2 each and pencils were sold at 3 for $1. How many pencils did she buy?

Q2) There are 85 bowls of Bak Chor Mee for 80 people. Each adult eats 2 bowls of Bak Chor Mee and every three children share 1 bowl of Bak Chor Mee. How many adults and children are there?

Hope this helps.

Best wishes