Tutor MathsGuru: Ask me for your burning Maths questions!

[Vanilla Cake]

ck123:

The ratio of John's pencil to Mary's pencil was 4:3 After John transferred 80 pencils to Mary, the ratio was 4:7

How many pencils did they have altogether?

Using ratio based on unchanged total concept to solve:

Before
J : M
4 :3
44 :33

After
4 : 7
28 : 49

Note that in terms of ratio-total (before): 4+3 =7 and total (after):4+7=11.
Equate both of them by multiply \"before\" by 11 and multiply \"after\" by 7.
Now, both of them are equal (\"before\":44+33=77 and \"after\":28+49=77)

John transferred 80 pencils to Mary->( 44-28 ) units = 16 units
16 units = 80
77 units = 385

Number of pencils that they had altogether was 385

[ck123]

Hi vanilla,


Got it. Thanks.

[Guan Hui]

ck123:

Hi all,


Please help,

The ratio of John's pencil to Mary's pencil was 4:3 After John transferred 80 pencils to Mary, the ratio was 4:7
How many pencils did they have altogether?

Thanks

the total amount nv change.
so the total or the ratio should be the same.
john:mary: total
4:3:7
4:7:11
lowest common multiple for 7 and 11 is 77
so the new ratio should be...
44:33:77
28:49:77

looking at john ratio.
44-28=16
but he need to give 80.
so 80/16=5

so the exact ratio will be
220:165:385
140:245:385

just by looking the ans is 385 pencils.

[nettie]

CoffeeCat:

nettie:

The question is
One coffee table and six identical chairs cost $2040. The coffee table cost $200 less than a chair. Find the cost of the coffee table.
Ans: $840.00
Working:
$200 x 6 = $1,200.00
$(2010-1200) = $840.00

But my boy insisted that the answer is $120.00
How to explain to him?

:?: :?:

have u asked ur boy insists? Perhaps he is right because 840 refers to the cost of 7 coffeetables. By minusing the extra cost of 200 6times u r left with cost of 7 coffeetables

confuse :?

But i feel that the answer his answer is correct too

[xxjustakidxx]

nettie:

CoffeeCat:

[quote=\"nettie\"]
The question is
One coffee table and six identical chairs cost $2040. The coffee table cost $200 less than a chair. Find the cost of the coffee table.
Ans: $840.00
Working:
$200 x 6 = $1,200.00
$(2010-1200) = $840.00

But my boy insisted that the answer is $120.00
How to explain to him?

:?: :?:

have u asked ur boy insists? Perhaps he is right because 840 refers to the cost of 7 coffeetables. By minusing the extra cost of 200 6times u r left with cost of 7 coffeetables

confuse :?

But i feel that the answer his answer is correct too :P[/quote]The answer IS 120 what. I've finished PSLE last year and I'm pretty sure of my answer.

[mathsguru]

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.

Hi Starlight1968sg,

Here are my solutions. Hope they help!


MathsGuru

http://www.postimage.org/image.php?v=PqzGQQ0

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

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

[mathsguru]

tisha:

At first, the ratio of Jane's savings to Devi's savings was 5:4. After each of them donated $60 to charity, the ratio became 13:10. What was Jane's saving at first?


This is a primary 5 Question. I know how to solve this using algebra, but need help with the heuristic method.

Hi Tisha,

Here's my solution.

Hope it is clear enough!


MathsGuru

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

[mathsguru]

nettie:

I found this question in ACS Primary 4 SA2 paper.


I am kinda of confuse too with the answer

The question is

One coffee table and six identical chairs cost $2040. The coffee table cost $200 less than a chair. Find the cost of the coffee table.

Ans: $840.00

Working:

$200 x 6 = $1,200.00
$(2010-1200) = $840.00

But my boy insisted that the answer is $120.00

How to explain to him?

:?: :?:

Hi Nettie,

The good news is...your boy is correct!

Think there's some typo in the answer. Here's my solution. You can approach the question from 2 angles.

Hope this clarifies your doubt!

Cheers,
MathsGuru

http://www.postimage.org/image.php?v=PqzKcR9

[mathsguru]

ck123:

Hi all,


Please help,

The ratio of John's pencil to Mary's pencil was 4:3 After John transferred 80 pencils to Mary, the ratio was 4:7
How many pencils did they have altogether?

Thanks

Hi Ck123,

Here's my solution.

Cheers,
MathsGuru

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

[mathsnerd]

Grace has a container of red and white ribbons. If she adds in 10 red ribbons, 60% of the ribbons in the container are white. If she adds in another 30 white ribbons, 75% of the ribbons in the container are white. How many red ribbons are in the container?


I need a solution for this question please! :? :?: