Tutor MathsGuru: Ask me for your burning Maths questions!

[BigDevil]

Andaiz:

BigDevil:

:oops: I knew how to work out the answer, but I couldn't quite explain myself.

If we encounter this kind of question in exams, is it sufficient to lay out the answer as I did, or must the students explain their work?

BigDevil, the devil is in the details...the students are told to put down the working and/or models coz in the event that the answer is wrong (copy wrong or just plain careless), the marker can follow the logic and trend of thoughts!

Thanks, Andaiz. Point noted! :salute:

[BigDevil]

mathsguru:

Don't worry, ur working is good enough to earn u full marks for this question. I added the explanation for Underthesea's reference.

That's good to hear, but glad to see your explanation. I foresee I would need to do some explaining to DD.

[mathsguru]

Hi all,


Just wanna share the solutions to some P3 questions I received from a fellow KSP member.

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

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

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

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

Cheers,
MathsGuru

[Dharma]

Solutions to JA’s questions.


Q1)Find the sum of the first 100 numbers in the following number sequence.
1,2,3,4,5,6,7,8,9,1,0,1,1,1,2,1,3,1,4,1,5,…

1 to 9 = 9 numbers
1,0,1,1,12…1,7,18,1,9 = 20 numbers
2,0,2,1,2,2…2,7,2,8,2,9 = 20 numbers
3,0,3,1,3,2…3,7,3,8,3,9 = 20 numbers
4,0,4,1,4,2…4,7,4,8,4,9 = 20 numbers
Total 89 numbers

Last 11 numbers : 5,0,5,1,5,2,5,3,5,4,5

Sum of 1st 100 numbers =
1+2+3+4+5+6+7+8+9+1+0+1+1+1+2+1+3+1+4+1+5+ …+ 5+1+5+2+5+3+5+4+5

(1+2+3+…+8+9) = 45
(1+0+1+1+1+2+…+1+8+1+9) = (1x10) + 45 = 55
(2+0+2+1+2+2+…+2+8+2+9) = (2x10) + 45 = 65
(3+0+3+1+3+2+ …+3+8+3+9) =(3x10) + 45 = 75
(4+0+4+1+4+2+…+4+8+4+9) = (4x10) + 45 = 85
(5+0+5+1+5+2+5+3+5+4+5) =(5x6) + 10 = 40

Sum = 45+55+65+75+85+40 = 365

Q2)The Sentosa High School’s telephone number is an eight digit number.The sum of the two numbers formed from the first three digits and the last five digits respectively is 66558.The sum of the two numbers formed from the first five digits and the last three digits is 65577.Find the telephone number of the The Sentosa High School.

Let the telephone number be abcdefgh

defgh + abc = 66558
(10000d + 1000e + 100f + 10g +h)+(100a + 10b + c) =60000 + 6000 + 500 + 50 + 8
d = 6
1000e + 100(f+a) + 10(g+b) + (h+c) = 6000 + 500 + 50 + 8 ………………(1)

abcde + fgh = 65577
(10000a + 1000b + 100c + 10d + e)+(100f + 10g +h) = 60000 + 5000 + 500 + 70 +7
a = 6
1000b + 100(c +f) + 10(d+g) + (e +h) = 5000 + 500 + 70 + 7 ……….(2)


From (1)
1000e + 100(f+6) +10(g+b) +(h+c) = 6000 + 500 + 50 + 8 …………….(3)
f+6 = 15; f = 9
Since f = 9; e = 5

From (2)
1000b + 100(c+9) + 10(6+g) + (4+h) = 5000 + 500 + 70 + 7 ……………(4)
C + 9 = 15; c = 6
Since c = 6; b = 4

From (3)
5000 + 1500 + 10(g+4) + (h+6) = 6000 + 500 + 50 + 8
h+6 = 8
h=2
g+4 = 5
g=1

abcdefgh = 64665912

646 + 65912 = 66558… ok
64665 + 912 = 65577…ok

The telephone number is 64665912


Q3)Placed on a table is a maths problem
89+16+69+6X+Y8+88
X and Y represents a digit.
Two students A and B sit on the opposite sides of the table facing
each other.They read the problem from
their directions and both get the same answer.What is their answer?

89 + 16 + 69 + 6X + Y8 + 88 = 88 + 8Y + X9 + 69 + 91 + 68
262 + 6X + Y8 = 316 + X9 + 8Y
(6X + Y8 ) – (X9 + 8Y) = 54
X and Y can 1, 6, 8 or 9

1 and 8 looks the same when seen from both directions
6 will look like 9 to the person opposite and vice versa.

By trial and error, using X =1 & Y = 9

(61 + 98 ) – (19 + 86) = 54 —ok
89+16+69+61+98+88 = 421

[Vanilla Cake]

Hi Mathsguru,


Pls refer to http://www.orlesson.org/orp/09Ma/2009-P6-Math-SA2-PeiChun.pdf. There are no given answers for Q13 to Q18 in paper 2.
Pls kindly provide the answers for these questions. Thanks in advance.
:love:

[speedmaths.012624com]

Leo and Tom are given some money each. If Leo and Tom spend $50 and $25 each day respectively, Leo still have $600 when Tom has spent all his money. If they spend $25 and $50 each day respectively, Leo will still have $1800 when Tom has spent all his money. How much money is given to Leo.


=
Hi,

The method to solve this type of question (and other tricky PSLE maths problem sums) can be found in the book \"Raffles Maths Tricks - Volume 1\", which is available at Popular Book store.

http://www.postimage.org/image.php?v=gxYh3kS

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

[YLH88]

Hi Mathsguru,


Need your help with the following 2 questions :

1) Tim gives 20% of his salary to his wife every month. There is an increase of 5% in his salary this month. Hence, the sum of money which he gives to his wife increases by $100.
a) How much money did he give to his wife last month ?
b) How much money does he earn each month after his pay rise ?


2) A writer writes a uniform number of words every week. He would delete 25% of his words at the end of every week. From last week onwards, the number of words he writes every week increases by 10%. As a result, the number of words he deletes at the end of the week increases by 300.
a) How many words did he write in a week originally ?
b) How many words did he delete last week ?


Thank you!

[YLH88]

[quote]Leo and Tom are given some money each. If Leo and Tom spend $50 and $25 each day respectively, Leo still have $600 when Tom has spent all his money. If they spend $25 and $50 each day respectively, Leo will still have $1800 when Tom has spent all his money. How much money is given to Leo.
[/quote]Hi,

For this question, how come we can't get the answer by using 2u + 600 = 1400 where 2u being the 1st part where we know the spending of Leo is $50 and Tom is $25 ?

Thank you.

[Tiramisu Coco]

Hi mathsguru,


Need your help with the following 2 qtns:

1) In a class, 16 of the pupils are boys. Then 3/4 of girls left the classroom.
If 1/6 of the original number of pupils are now girls, find the number of
pupils in the class at first.

2) The number of apples is 5/11 of the number of pears at a fruit stall. After
Mrs Fong bought half of the pears, there were a total of 189 apples and
pears left at the stall.

a) How many apples were there at the stall?

b) How many apples and pears were at the stall at first?


Thank you!

[mathsguru]

YLH88:

Hi Mathsguru,


Need your help with the following 2 questions :

1) Tim gives 20% of his salary to his wife every month. There is an increase of 5% in his salary this month. Hence, the sum of money which he gives to his wife increases by $100.
a) How much money did he give to his wife last month ?
b) How much money does he earn each month after his pay rise ?


2) A writer writes a uniform number of words every week. He would delete 25% of his words at the end of every week. From last week onwards, the number of words he writes every week increases by 10%. As a result, the number of words he deletes at the end of the week increases by 300.
a) How many words did he write in a week originally ?
b) How many words did he delete last week ?


Thank you!

Hi Jasmine,

Here are my solutions:

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

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

Cheers,
MathsGuru