Q&A - P4 Math

[HAPPYH]

sokk:

Hi,


I've a question that goes like this-

Each digit can be used only once.
Arrange the digits 2,4,7,8 and 9 in these boxes so as to get the largest and smallest possible products.

Largest product. : [ ][ ][ ] x [ ][ ] =
Smallest product : [ ][ ][ ] x [ ][ ] =

The answer is
872 x 94 = 81968 ( for the largest product)
489 x 27 = 13203. (for the smallest product)

The answer said that the method is by \"guess and check\". So wouldn't the students have a number of combinations to try out ?
Is there a more direct method in doing this kind of question rather than by guess and check ?


Thanks for helping me answer my question

Does anyone know the easier method / olympiad method to solve the above question? Thank you in advance.

[Xiao Hu]

:

Xiao Hu:

Hi Tianzhu, MathIzzzFun,


I have some questions on \"estimation\" that I hope you can help answer. I did a search with \"estimation\" but after going through 4 pages that don't have anything relating to my question, I decided to ask it here.

The question did not say estimate at which digit or which value.
Estimate 7281x39.
I think of 2 possible way to estimate
(1) ~7300 x 40
(2) ~7000 x 40
Mentally, it's so much easier and quicker to say (2) is a \"better\" estimation.

Anothe example:
Estimate 246 x 39
(1) ~250x40
(2) ~200 x 40

What's the rule or rules to teach our children when it comes to estimating?

TIA,
Xiao Hu

Hi

Estimation is taught so that the children understand how to do approximation. Students will not be asked to provide estimate of say 246 x 39 without given the bounds. For eg. a better estimate for 246 x 39 is 240 x 40 but normally we will approximate it to 250x 40 (which will provide the upper bound).
Usually, choices will be provided for estimate of product of two numbers, or the question will specifically state whether the answer/number is to be rounded to 10 or 100. Ffor eg. Jenny had twelve stamp books with same number of stamps in each book. The total number of stamps Jenny had was 3500 when rounded to the nearest 10. How many stamps did Jenny have ?

cheers.

Hi MathIzzzFun,
Thanks for your reply. Really appreciate your comments and giving an example of typical questions set. Very helpful!
I think the questions given to him was a good exercise on estimation! A real life situation where you have to decide how best to estimate.
Guess you are right, in exams, questions would probably state the boundaries.

Thanks,
Xiao Hu.

[chloecube]

found this in today Straits Time:


There were 255 balls in Box A, B and C. 36 balls were transferred from A to B, and 19 balls ere transferred from B to C. as a result, the number of balls in each box is the same. how many balls were in Box B at first.

Ans is 68.

tried but cant get the correct answer.

anyone cares to try?

[tianzhu]

chloecube:

found this in today Straits Time:


There were 255 balls in Box A, B and C. 36 balls were transferred from A to B, and 19 balls ere transferred from B to C. as a result, the number of balls in each box is the same. how many balls were in Box B at first.

Hi

Wow,Maths from the news.

You may draw some pictorial aids to show the transfer of balls.

The important point to note is that the total number of balls remains the same (255) before and after.

In the end, the number of balls in A, B and C is the same.

255/3 ----- 85 (number of balls in each box)

Consider box B.

36 balls in and 19 balls out

Hence 85 – 36 +19 ------ 68

Best wishes

[chloecube]

tianzhu:

chloecube:

found this in today Straits Time:


There were 255 balls in Box A, B and C. 36 balls were transferred from A to B, and 19 balls ere transferred from B to C. as a result, the number of balls in each box is the same. how many balls were in Box B at first.

Hi

Wow,Maths from the news.

You may draw some pictorial aids to show the transfer of balls.

The important point to note is that the total number of balls remains the same (255) before and after.

In the end, the number of balls in A, B and C is the same.

255/3 ----- 85 (number of balls in each box)

Consider box B.

36 balls in and 19 balls out

Hence 85 – 36 +19 ------ 68

Best wishes

Thks Tianzhu,

the article is abt the stress that kids in Singapore are facing now, they then give a few examples of the Math question that our P2 and P4 are getting.
after reading the article, i feel for the children, as quoted by one of the parent: \"the kid is learning how to cycle and juggle at the same time\"
i wish something can be done to lessen their work load. Children shld have a beautiful memories of childhood and not buried in books all day long.

if not for the help i got here, i doubt i ever solved those question

[Champion]

chloecube:

Thks Tianzhu,

the article is abt the stress that kids in Singapore are facing now, they then give a few examples of the Math question that our P2 and P4 are getting.
after reading the article, i feel for the children, as quoted by one of the parent: \"the kid is learning how to cycle and juggle at the same time\"
i wish something can be done to lessen their work load. Children shld have a beautiful memories of childhood and not buried in books all day long.

if not for the help i got here, i doubt i ever solved those question

Good Morning chloecube & Tianzhu :grphug:
Totally agree with chloecube; I have learnt and am still learning about Maths. Am so thankful that I can tips from this P4 Maths thread :salute: :salute:

[Nebbermind]

Champion:

chloecube:

Thks Tianzhu,

the article is abt the stress that kids in Singapore are facing now, they then give a few examples of the Math question that our P2 and P4 are getting.
after reading the article, i feel for the children, as quoted by one of the parent: \"the kid is learning how to cycle and juggle at the same time\"
i wish something can be done to lessen their work load. Children shld have a beautiful memories of childhood and not buried in books all day long.

if not for the help i got here, i doubt i ever solved those question

Good Morning chloecube & Tianzhu :grphug:
Totally agree with chloecube; I have learnt and am still learning about Maths. Am so thankful that I can tips from this P4 Maths thread :salute: :salute:

I think these parents are stressed coz they r not happy with a band-1 or A grade...they wanna A* or perfect100. I believe there are usually only a couple of such difficult questions unless u r from a premium school. Even if u don't get them right and get the rest correct, u should still get band-1.

[babies]

Hi any kind soul willing to help solving... :oops:


Q1: What is the smallest odd number that has only 3 factors?

Q2: Gary was given these numbers: 42, 50, 72, 84 and 96. Write down the sum of all the given numbers that have 2 and 6 as common factors.

:?: :? :?: :?

[tianzhu]

babies:

Hi any kind soul willing to help solving... :oops:


Q1: What is the smallest odd number that has only 3 factors?

Q2: Gary was given these numbers: 42, 50, 72, 84 and 96. Write down the sum of all the given numbers that have 2 and 6 as common factors.

:?: :? :?: :?

Hi

In answering these questions, it may useful to get your child to read the chapter on Factors in the school textbook.

Q1) The answer is 9 (1,3,9).

Q2) The number 50 does not have 6 as a common factor.
The sum of 42, 72, 84 and 96 is 294

Best wishes

[babies]

tianzhu:

babies:

Hi any kind soul willing to help solving... :oops:


Q1: What is the smallest odd number that has only 3 factors?

Q2: Gary was given these numbers: 42, 50, 72, 84 and 96. Write down the sum of all the given numbers that have 2 and 6 as common factors.

:?: :? :?: :?

Hi

In answering these questions, it may useful to get your child to read the chapter on Factors in the school textbook.

Q1) The answer is 9 (1,3,9).

Q2) The number 50 does not have 6 as a common factor.
The sum of 42, 72, 84 and 96 is 294

Best wishes

Hi tianzhu, thanks for your help,

But do you mind to explain in details for Q1 as I dont know how to get the steps done.

Thanks!