Tutor MathsGuru: Ask me for your burning Maths questions!

[Guan Hui]

girlmum I did a video response for you I hope it helps=D

http://www.youtube.com/watch?v=TUB9r2i2v0g

[mathsguru]

Vanilla Cake:

Hi Mathsguru,

Thanks for your helpful and useful explanations.1 more question [5 marks] from http://www.orlesson.org/orp/09Ma/2009-Math-SA1-SCGS.pdf which needs your model solution. Today, I checked through your earlier solutions in the 85+ pages of this thread but could not find something similar to this one.

A coin box contained some twenty-cent and fifty-cent coins in the ratio 4 : 3. After 20 twenty-cent coins were taken out to exchange for fifty-cents coins of the same value and put back in the box, the ratio of the number of twenty-cents coins to the number of fifty-cents coins became 7 : 11. Find the sum of money in the box.

Thanks again for your kindness in helping us.
When you have time, it's good to have your own blog to group your Maths solutions by topics. This will help us to search and look out for similar questions with your worked solutions before contemplating to post our new questions. Just my 2 cents worth.

Hi Vanilla Cake,

Here are my solutions. I came up with 2 methods, but none of them involve models. Not all ratio questions require models to solve. With more practice, your sis will be able to identify which kind of solution suit which kind of question. Hope the solutions are clear enough for your sis!

And hope in near future, I'll be able to set up a blog like what you suggested. :politebleah:

Cheers,
MathsGuru

http://www.postimage.org/image.php?v=aVi98cA

http://www.postimage.org/image.php?v=aVi9aHJ

[mathsguru]

girlmum:

Hi Mathguru,


Pls help to draw the model for this P3 maths question:

1) Mrs Chan had 20 pencils. She gave each pupil 4 pencils.
a) How many pupils did she give the pencils to? Ans : 5
b) If each child broke 1 pencil, how many pencils were not
broken? Ans : 15

My DD2 knows how to do the number sentences but not the model. Pls assist. :?: Thanks.

Hi Girlmum,

Actually, number sentences are good enough for these questions as they are rather straightforward.

Although models are useful tools in solving questions, there's no need to draw models for every problem sum. Different problems require different methods of solving.

In any case, here's the diagrams. Hope your gal can understand these questions better after looking at the diagrams!

Cheers,
MathsGuru

http://www.postimage.org/image.php?v=PqwFu59

[girlmum]

Hi Mathsguru,


:thankyou: for your help.

[Hifive]

Hi Mathsguru


Need your help with the following questions:

1. At the beginning of a wedding banquet, there were twice as many female guests as male guests. After 40 female and 30 male guests left, the ratio of the remaining number of females to the remaining number of male guests were 9:4. How many more female than male guests attended the wedding?

2. In city A, every household has either one or two computers. The ratio of the number of households to the number of computers is 3: 5. What fraction of the household has only one computer?


Thanks in advance.

[mathsguru]

Hifive:

Hi Mathsguru


Need your help with the following questions:

1. At the beginning of a wedding banquet, there were twice as many female guests as male guests. After 40 female and 30 male guests left, the ratio of the remaining number of females to the remaining number of male guests were 9:4. How many more female than male guests attended the wedding?

2. In city A, every household has either one or two computers. The ratio of the number of households to the number of computers is 3: 5. What fraction of the household has only one computer?

Thanks in advance.

Hi Hifive,

Here are my solutions. Hope they can help!


MathsGuru

http://www.postimage.org/image.php?v=PqwTv4J

http://www.postimage.org/image.php?v=PqwTxzS

[starlight1968sg]

Hi mathsguru,

I need your help again.

Q1) Nathan is reading a book which has its pages numbered 1 to 150. What is the total number of digits used to number the pages?

Q2) Junwei’s watch was 1 minute faster while Junhong’s watch was 2 minutes slower every hour. At a certain time, both watches were reset to the correct time. At the same moment on the same day, Junwei’s watch showed 5pm while Junhong’s watch showed 4pm. What should the correct time be at that moment?

Q3) Lance answered 50 questions in a quiz. For each correct answer, 3 points were awarded. For each incorrect answer, 1 point was deducted. If he scored a total of 114 points, how many questions did Lance answer correctly?

The above questions are from p5 maths school worksheets.

MTIA.

[Guan Hui]

starlight1968sg,


Q1)
pg 1 to 9=9 no. x 1=9 digits
pg 10 to 99= 90 no. x 2=180digits
pg 100 to 150= 51 no. x 3 = 153 digits
9 +180+153= 342digits

Q2)
5 pm and 4pm is 1 hr difference
junhong slow 2 min while junwei faster 1 min
so the time is 4.40pm

Q3)
3 steps guess n check
50 correct 0 wrong 150 pts(1st guess)
49 correct 1 wrong 146 pts(2nd guess)
150 -146=4 pts
150-114=36 pts
36/4=9
41 correct 9 wrong 114 pts(3rd guess)
ans: 41 correct

[starlight1968sg]

Guan Hui:

starlight1968sg,


Q1)
pg 1 to 9=9 no. x 1=9 digits
pg 10 to 99= 90 no. x 2=180digits
pg 100 to 150= 51 no. x 3 = 153 digits
9 +180+153= 342digits

Q2)
5 pm and 4pm is 1 hr difference
junhong slow 2 min while junwei faster 1 min
so the time is 4.40pm

Q3)
3 steps guess n check
50 correct 0 wrong 150 pts(1st guess)
49 correct 1 wrong 146 pts(2nd guess)
150 -146=4 pts
150-114=36 pts
36/4=9
41 correct 9 wrong 114 pts(3rd guess)
ans: 41 correct

Hi guanhui,
Thanks for your prompt reply.
Q1 is very clear to me (why didn't I think of it? :roll: ).
Q3 should be ok though I dislike guess and check method.
Q2 is a bit tricky and can you please offer more explanation as how to get 4.40pm?
MTIA again.

[Guan Hui]

1 hr >>60 mins

for their time to be difference in 1 hr, jun hong watch must lag 40 mins while junwei watch must be fasten 20 mins. This is due to the speed the watches lag and fasten(is there such a word haha).

you can also say junhong is 2 unit and junwei 1 unit base on the ratio 2min is to 1 min. so 60/3= 20 min per unit.

jun wei 1 unit>>> watch is faster than actual 20 mins.
his watch show 5pm so... 4.40pm.
junhong 2 units>> watch lag by actual 40 mins.
his watch show 4pm so... 4.40pm also.
does this helps?? :roll: