Tutor MathsGuru: Ask me for your burning Maths questions!

[MathIzzzFun]

marcusya:

Hi,

can u lift some of my burden by help me solve this math question below ? Thanks in advance.

Issac had 200 more marbles than Alfred . In the first game issac lost 60% of his marbles. To Alfred . In the second game ,alfred lost 25% of his marble to issac . In the end , issac had 118 marbles leas than Alfred . How many marbles does Alfred have at first ?

Hi marcusya,

hope this helps

http://i55.tinypic.com/9uruq9.jpg\">

cheers.

[marcusya]

Thanks

[andante]

I have come across the following question which is Pei Hwa 2009 Prelim Paper 1 Q29, however I think the model answer given as 360 is not correct. Pls advise.


Clement had a wooden block measuring 50 cm by 70 cm by 90 cm. He wanted to cut out some little cuboids mesauring 2 cm by 3 cm by 4 cm. What was the minimum amount of wood wasted ?

In fact, I found discussion on this question, someone show the working for 360 cm3 and some suggested 180 cm3 but I thought that the answer can be even smaller than that.

Thanks.

[MathIzzzFun]

andante:

I have come across the following question which is Pei Hwa 2009 Prelim Paper 1 Q29, however I think the model answer given as 360 is not correct. Pls advise.


Clement had a wooden block measuring 50 cm by 70 cm by 90 cm. He wanted to cut out some little cuboids mesauring 2 cm by 3 cm by 4 cm. What was the minimum amount of wood wasted ?

In fact, I found discussion on this question, someone show the working for 360 cm3 and some suggested 180 cm3 but I thought that the answer can be even smaller than that.

Thanks.

Hi andante,

I sliced it down to 2 x 2 x 6 = 24 cm3 left.

cheers.

[MathIzzzFun]

andante:

I have come across the following question which is Pei Hwa 2009 Prelim Paper 1 Q29, however I think the model answer given as 360 is not correct. Pls advise.


Clement had a wooden block measuring 50 cm by 70 cm by 90 cm. He wanted to cut out some little cuboids mesauring 2 cm by 3 cm by 4 cm. What was the minimum amount of wood wasted ?

In fact, I found discussion on this question, someone show the working for 360 cm3 and some suggested 180 cm3 but I thought that the answer can be even smaller than that.

Thanks.

Hi andante,

here's how I did it

http://i55.tinypic.com/ht7ng1.jpg\">

cheers.

[KSP]

ksi:

youngtay:

Hi, please help


Larry planted some mango trees in a row with the same distance apart.
The distance between the first and the fifth tree was 40m.

a) Find the distance between the first and the tenth tree? (Ans:90m)
b) Find the distance between the fifth and the 50th tree? (Ans: 450m)

need help for b) why ans is 450m?

TIA

(a) 10-1 = 9 gaps in between Hence 9x 10 = 90m

(b) 10-5 = 5 gaps in between. Hence 5x10 = 50m
for every 10th-20th, 20th-30th, 30th-40th, 40th-50th trees, they are 10gaps each so 10x10m apart for each, so is 100m x 4 = 400m

Hence you get 400+50 = 450m.


What answer did you get?

ksi, are u a maths teacher ot tutor? :celebrate:

[andante]

MathIzzzFun:

andante:

I have come across the following question which is Pei Hwa 2009 Prelim Paper 1 Q29, however I think the model answer given as 360 is not correct. Pls advise.


Clement had a wooden block measuring 50 cm by 70 cm by 90 cm. He wanted to cut out some little cuboids mesauring 2 cm by 3 cm by 4 cm. What was the minimum amount of wood wasted ?

In fact, I found discussion on this question, someone show the working for 360 cm3 and some suggested 180 cm3 but I thought that the answer can be even smaller than that.

Thanks.

Hi andante,

here's how I did it

http://i55.tinypic.com/ht7ng1.jpg\">

cheers.

Why do you cut into 35x11x30 but not 35x12x30 ?
If I cut it into 35x12x30 and further cut the rest into 22x23x1, I will have 4cm3 left, not sure whether it is correct.

BTW, this question needs to explore all possibilities in order to know which is the minimum and if it is so, then I think it is no demanding and too much for the little mark awarded.

Pls advise.

[MathIzzzFun]

andante:

MathIzzzFun:

[quote=\"andante\"]I have come across the following question which is Pei Hwa 2009 Prelim Paper 1 Q29, however I think the model answer given as 360 is not correct. Pls advise.


Clement had a wooden block measuring 50 cm by 70 cm by 90 cm. He wanted to cut out some little cuboids mesauring 2 cm by 3 cm by 4 cm. What was the minimum amount of wood wasted ?

In fact, I found discussion on this question, someone show the working for 360 cm3 and some suggested 180 cm3 but I thought that the answer can be even smaller than that.

Thanks.

Hi andante,

here's how I did it

http://i55.tinypic.com/ht7ng1.jpg\">

cheers.

Why do you cut into 35x11x30 but not 35x12x30 ?
If I cut it into 35x12x30 and further cut the rest into 22x23x1, I will have 4cm3 left, not sure whether it is correct.

BTW, this question needs to explore all possibilities in order to know which is the minimum and if it is so, then I think it is no demanding and too much for the little mark awarded.

Pls advise.[/quote]Hi andante,

50 cm x 70 cm x 90 cm / (2 cm x 3 cm x 4 cm) = 13125 blocks. So, it is not possible to have 4 cm3 left over.

When it is cut into 35x12x30 blocks, the block left is 2 cm x 90 cm x 70 cm, with this block, can only cut into 1 x 30 x 17 blocks leaving behind a block of 2 cm x 90 cm x 2 cm block ie 360 cm3.

cheers.

[andante]

MathIzzzFun:

Hi andante,


50 cm x 70 cm x 90 cm / (2 cm x 3 cm x 4 cm) = 13125 blocks. So, it is not possible to have 4 cm3 left over.

When it is cut into 35x12x30 blocks, the block left is 2 cm x 90 cm x 70 cm, with this block, can only cut into 1 x 30 x 17 blocks leaving behind a block of 2 cm x 90 cm x 2 cm block ie 360 cm3.

cheers.

Hi,
When it is first cut into 35x12x30 blocks, the block left is 2x90x70, that is right. But there are two ways to cut it. your solution of 360cm3 is one of the ways. The second way to cut it will generate 22x23x1 block i.e. 90 cut into 22x4 with remaining of 2cm and 70 cut into 23x3 with remaining of 1 cm which produces wastage of 1x2x2 = 4cm. (hope that I did not miss it anything)

[MathIzzzFun]

andante:

MathIzzzFun:

Hi andante,


50 cm x 70 cm x 90 cm / (2 cm x 3 cm x 4 cm) = 13125 blocks. So, it is not possible to have 4 cm3 left over.

When it is cut into 35x12x30 blocks, the block left is 2 cm x 90 cm x 70 cm, with this block, can only cut into 1 x 30 x 17 blocks leaving behind a block of 2 cm x 90 cm x 2 cm block ie 360 cm3.

cheers.

Hi,
When it is first cut into 35x12x30 blocks, the block left is 2x90x70, that is right. But there are two ways to cut it. your solution of 360cm3 is one of the ways. The second way to cut it will generate 22x23x1 block i.e. 90 cut into 22x4 with remaining of 2cm and 70 cut into 23x3 with remaining of 1 cm which produces wastage of 1x2x2 = 4cm. (hope that I did not miss it anything)

Hi andante,

when the remaining block is cut into 22 x 23 x 1 blocks, the remaining wood consists of an L-shaped block which can be cut into two blocks as shown. The wastage would be 456 cm3.

http://i52.tinypic.com/34zhw81.jpg\">


cheers.