Tutor MathsGuru: Ask me for your burning Maths questions!

[starlight1968sg]

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:

Yes, this helps a lot.
Thanks a lot, Mr guanhui!

[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.

[Hifive]

Hi mathsguru


Many thanks for your help !

Regards

[starlight1968sg]

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,
5:4 = 10:8 = 15:12.

After giving an equal amount of $60 (ie equal share), the new ratio is 13:10.

So the original ratio is 15: 12 because both after giving away 2 parts, the resulting ratio is 13:10.

This 2 parts correspond to $60 ie 1 part is $30.
Originally, Jane has 15 parts and thus she has $450 at first.

[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?

:?: :?:

[tisha]

starlight1968sg:

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,
5:4 = 10:8 = 15:12.

After giving an equal amount of $60 (ie equal share), the new ratio is 13:10.

So the original ratio is 15: 12 because both after giving away 2 parts, the resulting ratio is 13:10.

This 2 parts correspond to $60 ie 1 part is $30.
Originally, Jane has 15 parts and thus she has $450 at first.

Thank you very much for the solution.
So it is like tabulation/plug-n-play.
We need to generate the equivalent ratios of 5:4 (as in 10:8, 15:12 ...)till the difference of both their (Jane's and Devi's) share is equal, in this case we get it in just 2 tries ie 15:12.

Is there any model diagram approach to the same problem?

[Guan Hui]

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?

:?: :?:

lets take the table as 1 unit
so 1 chair is 1u+200
6 chairs>>> 6u+1200
plus the table...
Total cost=7u+1200=2040
1u=$120

check:
table =$120
chair =$120+200=$320
6 chairs= 6 x 320=$1920
$1920+$120= $2040=Total (means correct)

your boy is correct

[Guan Hui]

tisha:

starlight1968sg:

[quote=\"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,
5:4 = 10:8 = 15:12.

After giving an equal amount of $60 (ie equal share), the new ratio is 13:10.

So the original ratio is 15: 12 because both after giving away 2 parts, the resulting ratio is 13:10.

This 2 parts correspond to $60 ie 1 part is $30.
Originally, Jane has 15 parts and thus she has $450 at first.

Thank you very much for the solution.
So it is like tabulation/plug-n-play.
We need to generate the equivalent ratios of 5:4 (as in 10:8, 15:12 ...)till the difference of both their (Jane's and Devi's) share is equal, in this case we get it in just 2 tries ie 15:12.

Is there any model diagram approach to the same problem?[/quote]I just found this method while tuitioning...
you may want to try if this is easier..

5:4 after giving $60 each becomes 13:10
this means that the 1st ratio(5:4) should be bigger.(cause 5:4 - to become 13:10)
similarly to starlight1968sg, we multiply it
10:8(still smaller)
15:12(finally bigger)
we can just use 1 side of the ratio.
15 to become 13 we actually -2
we need to -60
which is 30times of -2.
so both ratio x30
(after this step we find the exact value of money from beginning to end)
450:360
390:300
just from looking we can see its $450.

[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

[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