Tutor MathsGuru: Ask me for your burning Maths questions!

[Herbie]

There were some chairs in a school hall. 1/2 of the chairs were placed in short rows while 2/5 of the chairs were placed in long rows. The rest of th chairs were stacked at the back of the hall.


There were 15 short rows and 8 long rows. If each short row contained 7 chairs less tha each kong rows, how many chairs were there in the wall altogether.

Sorry, there is a typo error. There shld be 8 long rows.

[Dharma]

Herbie:

There were some chairs in a school hall. 1/2 of the chairs were placed in short rows while 2/5 of the chairs were placed in long rows. The rest of th chairs were stacked at the back of the hall.


There were 15 short rows and 8 long rows. If each short row contained 7 chairs less tha each kong rows, how many chairs were there in the wall altogether.

Sorry, there is a typo error. There shld be 8 long rows.

Short rows : 15 rows x (1u) chairs per row = 15u chairs
Long rows : 8 rows x (1u + 7) chairs per row = (8u + 56) chairs

No. of chairs in short rows = ½ of total chairs (50%)
No. of chairs in long rows = 2/5 of total chairs (40%)
No. of chairs stacked = 10%

(8u + 56)/ 15u = 4/5
5(8u + 56) = 4(15u)
40u + 280 = 60u
20u = 280
1u = 14

Total no. of chairs = 30u = 30 x 14 = 420

[YLH88]

[quote]YLH88 wrote:

1) In the figure below, which is not drawn to scale, 1/5 of the circle is shaded. The ratio of the area of the square to the sum of area of the rectangle and the circle is 1 : 2. 60% of the square is shaded. 1/3 of the rectangle is shaded. What is the ratio of the area of the circle to the square to the rectangle ?

Vanilla Cake wrote :
Area of square : Area of rectangle+Area of circle
1 : 2
10 : 20 [/quote]
Hi Vanilla Cake,

May I know why you change the ratio for area of square : area of Rectangle + Area of circle from 1 : 2 to 10 : 20 ?

[kitty2]

Please help to solve these questions,thanks.


1)Audrey and Belle have some money each.If Audrey spends $18 and Belle spends $24 each day.Audrey will have $25 left.when belle has spent all her money.If Audrey spends $13 and belle spends $30 each day,Audrey will still have $139 left.when Belle has spent all her money.How much money do they have altogether?

2)Figure No of cakes

1 1
2 4
3 10


a)How many cubes will ther be in Fig 6?

b)Which figure will have 120 cubes?

[Vanilla Cake]

CoffeeCat:

Herbie:

Thanks VC and Dharma Can help with the qn below?


There were some chairs in a school hall. 1/2 of the chairs were placed in short rows while 2/5 of the chairs were placed in long rows. The rest of th chairs were stacked at the back of the hall.

There were 15 short rows and long rows. If each short row contained 7 chairs less tha each kong rows, how many chairs were there in the wall altogether?

Tx

Is there an answer key for this?
At first based on this \"There were 15 short rows and long rows.\", I take it that there are a total of 15 rows altogether.
Unless I am mistaken, this interpretation though interesting, only secondary mo technique can yield the answer of 630. Otherwise guess-and-check will be much easier. Unless this is what the school intended to test upon.
So perhaps it would make sense if it was 15 short and 15 long rows.

Hi CoffeeCat
Refer to Herbie's post dated 05 May 2010 08:10, this question was wrongly typed but it is still possible to solve using basic algebra at P6 level to solve the wrongly typed question by Herbie. Correct me if I am wrong and pls check the logic flow of my workings.

There were some chairs in a school hall. 1/2 of the chairs were placed in short rows while 2/5 of the chairs were placed in long rows. The rest of th chairs were stacked at the back of the hall.
There were 15 short rows and long rows. If each short row contained 7 chairs less tha each kong rows, how many chairs were there in the wall altogether?

Look for the unknown which is the total number of chairs in the hall and assume that it is C.

Number of Chairs
Short rows: 1/2 = 50% -> 0.5C
Long rows: 2/5 = 40% -> 0.4C

Assume the number of short rows to be S and the number of long rows to be 15-S

Difference between the chairs in the short rows and long rows = 0.5C-0.4C = 0.1C
Difference between number of chairs in a short row and a long row = 7

7S = 0.1C
35S = 0.5C
28S = 0.4C

Form an equation based on info given by the question:
0.5C/S + 7 = 0.4C/(15-S)
(0.5C+7S)/S = 0.4C/(15-S)
(35S+7S)/S = 28S(15-S)
42S/S = 28S/(15-S)
28S² = 42S(15-S)
28S² = 630S-42S²
70S² = 630S
70S = 630
S = 9

Sub S = 9 into 0.5C/S + 7 = 0.4C/(15-S)

0.5C/9 + 7 = 0.4C(15-9)
0.5C/9 + 7 = 0.4C/6
C + 126 = 1.2C
0.2C = 126
C = 630

There were 630 chairs in the hall altogether.

Submitted by VC's mum.

[Vanilla Cake]

kitty2:

1)Audrey and Belle have some money each.If Audrey spends $18 and Belle spends $24 each day.Audrey will have $25 left.when belle has spent all her money.If Audrey spends $13 and belle spends $30 each day,Audrey will still have $139 left.when Belle has spent all her money.How much money do they have altogether?


2)Figure No of cakes

1 1
2 4
3 10

a)How many cubes will ther be in Fig 6?
b)Which figure will have 120 cubes?

Hi kitty2,
Pls refer to the links below while waiting for Mathsguru's solutions:

http://psle2010a.blogspot.com/2010/03/14.html
http://psle2010a.blogspot.com/2010/03/mathsp62009sa1p2ny.html
http://www.onsponge.com/forum/35-thinkingmathonsponge/2528-p6-maths.html
http://www.onsponge.com/forum/35-thinkingmathonsponge/1917-p6-maths-2009-nanyang-sa1-paper-2.html

Submitted by VC's mum.

[Vanilla Cake]

YLH88:

[quote]YLH88 wrote:

1) In the figure below, which is not drawn to scale, 1/5 of the circle is shaded. The ratio of the area of the square to the sum of area of the rectangle and the circle is 1 : 2. 60% of the square is shaded. 1/3 of the rectangle is shaded. What is the ratio of the area of the circle to the square to the rectangle ?
Vanilla Cake wrote :
Area of square : Area of rectangle+Area of circle
1 : 2
10 : 20

Hi Vanilla Cake,
May I know why you change the ratio for area of square : area of Rectangle + Area of circle from 1 : 2 to 10 : 20 ?[/quote]Hi YLH88,
I am VC's mum and VC won't be back home today until 7 pm plus due to SMO training and dance practice.
Sorry for the inconvenience caused due to VC's inadequate explanation as she is still a Sec 2 girl.

Area of square : Area of rectangle+Area of circle
1 : 2
Multiply by 10
10 : 20

because 60% of the square is shaded.60% = 3/5.
Instead of 1x 3/5 which will be inconvenient as 3/5 unit, expand the ratio by multiplying by 10. So, 10x3/5 = 6 units which is easier to calculate.

Hope this helps.
Submitted by VC's mum

[kitty2]

Vanilla Cake:

kitty2:

1)Audrey and Belle have some money each.If Audrey spends $18 and Belle spends $24 each day.Audrey will have $25 left.when belle has spent all her money.If Audrey spends $13 and belle spends $30 each day,Audrey will still have $139 left.when Belle has spent all her money.How much money do they have altogether?


2)Figure No of cakes

1 1
2 4
3 10

a)How many cubes will ther be in Fig 6?
b)Which figure will have 120 cubes?

Hi kitty2,
Pls refer to the links below while waiting for Mathsguru's solutions:

http://psle2010a.blogspot.com/2010/03/14.html
http://psle2010a.blogspot.com/2010/03/mathsp62009sa1p2ny.html
http://www.onsponge.com/forum/35-thinkingmathonsponge/2528-p6-maths.html
http://www.onsponge.com/forum/35-thinkingmathonsponge/1917-p6-maths-2009-nanyang-sa1-paper-2.html

Submitted by VC's mum.

:thankyou:

[i-mum]

Hi MathsGuru,


1. A, B & C shared some sweets. A received 1/11 of the sweets. B received 1/4 of the number of sweets C received. When C gave away 104 sweets to be shared between A and B, they found that all of them had the same number of sweets. How many sweets were there at first?

2. A, B and C shared a sum of money.
A’s share was 1 1/2 timess that of B and B’s share was 1 1/4 times that of C.
(a) what fraction of A’s share was C?
(b) If A gave B $19 and C $22, A would have as much money as C. Find the sum of money shared.

Thank You.

i-mum

[Dharma]

i-mum:

Hi MathsGuru,


1. A, B & C shared some sweets. A received 1/11 of the sweets. B received 1/4 of the number of sweets C received. When C gave away 104 sweets to be shared between A and B, they found that all of them had the same number of sweets. How many sweets were there at first?


i-mum

Q1)
A & B : 3u + 104 = 2p

C : 8u – 104 =1p

16u - 208 = 3u + 104
13u = 312
1u = 24

Total no. of sweets at first = 24 x 11 = 264


Q2)
A: 15u
B: 10u
8u

(a)\tFraction = 8/15b)\t

A : 15u - $41 = 1p
C : 8u + $22 = 1p

(b)
15u - $41 =8u + $22
7u = $63
1u = $9

Sum of money shared = 15u + 10u + 8u = 33u = 33 x $9 = $297