Tutor MathsGuru: Ask me for your burning Maths questions!

[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

[Vanilla Cake]

starlight1968sg:

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?

Suppose Lance answered all 50 questions correctly, he would score:50x3=150 points.
In the end, he scored a total of 114 points meaning to say that he lost 36 marks.
For every incorrect answer that he had answered, he lost 4 points (1 point was deducted and didn't get 3 points for the correct answer)
So, he answered (36/4) = 9 questions incorrectly.
Number of questions that Lance answered correctly was 50-9=41

[tisha]

Vanilla Cake:

starlight1968sg:

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?

Suppose Lance answered all 50 questions correctly, he would score:50x3=150 points.
In the end, he scored a total of 114 points meaning to say that he lost 36 marks.
For every incorrect answer that he had answered, he lost 4 points (1 point was deducted and didn't get 3 points for the correct answer)
So, he answered (36/4) = 9 questions incorrectly.
Number of questions that Lance answered correctly was 50-9=41

Using tabulations it is easy to solve this problem. It will also be easy for the child to understand. You can start by 25 correct and 25 wrong. And then depending on the answer increase or decrease accordingly. Should be solved in 3 to 4 iterations.

[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