Tutor MathsGuru: Ask me for your burning Maths questions!

[mathsguru]

tamarind:

Thanks in advance. My friend sent me this question :


I am a three digit number. The digit in the tens place is 6 less than the digit in the hundreds place. The tens place is 2 more than the digit in the ones place. If the digit in the ones place is 5, then I am the number ______.

Hi there Tamarind,

At first glance, ur question looks pretty simple, but when I looked at it in detail, I had the same conclusion as the above 2 folks.

Is there a typo in the question given to u? If the digit in the tens place is 6 less than the digit in the hundreds place, u can never get a 3-digit no. Perhaps it's \"6 more than\"? Because if it is really 6 less, then the digit in the hundreds place could take 9, 8, 7 or 6 only. And the corresponding digit in the tens place will be 3, 2, 1 or 0, which are all less than 5.

If it is \"6 more than\", working backwards should give u the answer easily.

Digit: 5
Tens: 5 + 2 = 7
Hundreds: 7 - 6 = 1
Answer: 175.

Or if it's \"the tens place is 2 less than the digit in the ones place\", then the answer will be 935.

Should anyone know how else to solve this, assuming the original question is correct, pls share ur answer here. I would love to learn sth new too.

Regards,
MathsGuru

[mathsguru]

KSP:

Hi mathsguru,


How much time is allocated for such question like this in real exam?

Hi KSP,

I would say this kind of question is usually found in the last few pages of Paper 2 and is worth about 5 marks. It's true that for most students, they will have to take some time to think through and solve (probably about 15 min). But that's the way our Primary Maths standard is...and it's getting harder and harder all the time.

What I would suggest is for students to practise more of such \"thinking\" questions during the year and get used to the problem-solving technique so that in exam, they can solve it within a reasonable amt of time, say 7 - 10 min.

Regards,
MathsGuru

[tamarind]

Dear all who replied to my question,

My friend said it is from an assessment book. The answer is not 175.

I just wanted to confirm that there is something wrong with this question. The publisher need to correct this mistake.

[Tang]

mathsguru:

suiyuan:

2)Mr Lim spent $1496 on some comics and dictionaries altogether. The number of comics bought to the number of dictionaries bought was in the ratio of 3 : 2. A dictionary cost $4 more than a comic. The total cost of the comics was 20% more than the total cost of the dictionaries. Find the cost of a dictionary.

Hi Suiyuan,

As promised, here's my detailed diagrams and working. Hope it's self-explanatory enough.

Regards,
MathsGuru

http://www.postimage.org/image.php?v=Pq1zUxsr

Number C : D = 3 : 2
--------------
Unit price
C [ ]
D [ ][$4]
--------------
Total cost
C [ ][ ][ ]
D [ ][ ][$8]

3u = 1.2 x (2u + 8 )
0.6u = 9.6
1u = 16

D = 4 + 16 = $20

The cost of a dictionary was $20.

[atutor2001]

mathsguru:

Hi KSP,

.....they can solve it within a reasonable amt of time, say 7 - 10 min....

Regards,
MathsGuru

Cannot lah. This is one of those \"NORMAL questions\". If want to get good results must solve in less than 5 min you know - no need to think one, see only must know how to just do one. That's why last thought my kid about 6 years ago now still can remember this type of question.

[mathsguru]

atutor2001:

Cannot lah. This is one of those \"NORMAL questions\". If want to get good results must solve in less than 5 min you know - no need to think one, see only must know how to just do one. That's why last thought my kid about 6 years ago now still can remember this type of question.

Well, since you know it so well, then my answer is inconsequential.

[Seekinghelp]

Hi Mathguru,

I would like to check with u the ques of this; A sausage roll was cut into 5 equal pieces. Shu Qin took a piece and ate 1/2 of it. What fraction of the sausage roll was not eaten? Ans: 2/5 rite? It’s a P2 assessment book. Because the ans that was given seems different from mine and I dun have much confidence in myself.

[mathsguru]

Seekinghelp:

Hi Mathguru,

I would like to check with u the ques of this; A sausage roll was cut into 5 equal pieces. Shu Qin took a piece and ate 1/2 of it. What fraction of the sausage roll was not eaten? Ans: 2/5 rite? It's a P2 assessment book. Because the ans that was given seems different from mine and I dun have much confidence in myself.

Hi Seekinghelp,

The answer should be 9/10.

Here's my working:
Each piece of sausage = 1/5
Amount Shu Qin ate = 1/2 x 1/5 = 1/10
Fraction of sausage that was not eaten = 1 - 1/10 = 9/10

Hope this helps. Let me know if you need further explanation ya...

Enjoy the rest of your weekend,
MathsGuru

[Seekinghelp]

Ty for yr explanation but I still dun get it. Is it possible u draw out the model and show me? Btw, yr ans is correct. So sry still need to ask u 1 more ques.


Tank A had 345 litres of water more than Tank B. Tank B had 500 litres of water less than Tank C. How much more water was there in Tank C than in Tank A? This ques is extracted fr 1 of the school exam ques but I duno how to explain it to my nephew, is it possible u show me with model drawing too?

[Muffins]

Seekinghelp:

Ty for yr explanation but I still dun get it. Is it possible u draw out the model and show me? Btw, yr ans is correct. So sry still need to ask u 1 more ques.


Tank A had 345 litres of water more than Tank B. Tank B had 500 litres of water less than Tank C. How much more water was there in Tank C than in Tank A? This ques is extracted fr 1 of the school exam ques but I duno how to explain it to my nephew, is it possible u show me with model drawing too?

Hi Seekinghelp, I can solve your problems for you!

If 1 sausage roll is cut into 5 equal pieces, then one piece will be 1/5 of the full sausage roll. Half of 1/5 is 1/10, so 1 - 1/10 = 9/10...

For your second question, it can be done like this. Tank A = Tank B + 345 litres. Tank C = Tank B + 500 litres (Tank B = Tank C - 500 litres). So, (Tank B + 500 litres) - (Tank B + 345 litres) = 500 litres - 345 litres = 155 litres.

Hope I helped!