Q&A - P5 Math

[tianzhu]

Chan09:

1) mr tan monthly salary is twice mr lee. His monthly savings is 6 times mr lee. Given both of them spend $1000 monthly, how much money does mr tan earn?
Ans 2500

Hi

You may use MD or Units Method.

Salary
Mr Tan ----- 2 --------- 10
Mr Lee ----- 1---------- 5
Difference -----1------ 5

Monthly savings
Mr Tan ----- 6
Mr Lee ----- 1
Difference ----- 5 ------ 5

Since they spent the same amount of $1000 monthly, the difference in the amount of money stays the same (Constant Difference)

Make the difference in number of units the same.

10 - 6 ----- 4
(5 - 1 ----- 4)

4 units ----- 1000

1 unit ----- 250

10 units ------ 2500 (Mr Tan’s salary)

Best wishes

[tianzhu]

Chan09:

2) out of the 40000 people, 30% were women, 10% children and rest men. Some women left the show with half the no. Of children before it ended. As a result the % of men increased to 75% of the people at the show at the end. How many women were at the show at the end?
Ans 6000

At first
Women ----- 30% ------ 12000
Children ----- 10% ------ 4000
Men ------ 60% ------- 24000

In the end
Children ------ 2000
Men ------ 24000 (75%)

75% ------ 24000
1% ------ 320

Women ------ 25% ------- 8000

Number of women at the end of the show ------ 8000 – 2000 ------ 6000

Best wishes

[peggy]

Hi,


kindly assist this question from school.

Salmah, Titus and Umi shared a box of cards.
Salmah received 25% of what Titus and Umi received altogether.
Umi received 35% of the cards. If Salmah and Umi received 66 cards altogether, how many cards did Titus receive ?

I think I had seen similar question here somewhere but don’t seems to be able to locate it…

[lizawa]

peggy:

Hi,


kindly assist this question from school.

Salmah, Titus and Umi shared a box of cards.
Salmah received 25% of what Titus and Umi received altogether.
Umi received 35% of the cards. If Salmah and Umi received 66 cards altogether, how many cards did Titus receive ?

I think I had seen similar question here somewhere but don't seems to be able to locate it.....

Use ratio to solve.

S : T+U
= 25 : 100
= 1 : 4

U : S+T
= 35 : 65
= 7 : 13

Total units received by 3 of them should be the same. So convert
S : T+ U
= 1 : 4
= 4 : 16
(because 7 + 13 = 20 )

S : T : U
= 4 : 9 : 7
4u + 7u = 11u (S and U)
11u -> 66
1u -> 6
T: 9u -> 9 x 6 = 54.

[peggy]

Hi Lizawa,


Thanks for your prompt reply and clear explanations !!!

[Essential]

Hello Tian Zhu , hope you are there to help me.

I need your help to solve this question:-
1) Renjie has three ropes with length of 144cm , 168 cm and 252 cm. He wants to cut the three ropes into shorter pieces of equal length with no remainders. a) What is the greatest possible length of each of the shorter pieces ? b) how many of the shorter pieces of equal length can he get?

[tianzhu]

Essential:

Hello Tian Zhu , hope you are there to help me.

I need your help to solve this question:-
1) Renjie has three ropes with length of 144cm , 168 cm and 252 cm. He wants to cut the three ropes into shorter pieces of equal length with no remainders. a) What is the greatest possible length of each of the shorter pieces ? b) how many of the shorter pieces of equal length can he get?

Hi

Where is your question from?

The greatest possible length of each of the shorter pieces must be divisible by 144, 168 and 252.

So we are talking about the Highest common factor (HCF).

In this case, the greatest possible shorter length is 12.

(a)12 ----- for P5 syllabus, I think generally GC/ Logical reasoning is used to find the common factor.

Consider the shorter piece of 144cm; the possible shorter lengths are 144*1, 72*2, 36*4, 24*6, 12*12, 6*24.
Out of 144, 72,36,24,12, only 12 is divisible by 144, 168 and 252.

(b) 252/12 ------ 21, 168/12 ----- 14 and 144/12 ----- 12

Number of shorter pieces -----21+14+12 ------ 47

Best wishes

PS ----- HCF is covered in Secondary One Maths.

A good website to learn more about HCF.
http://mssia.wordpress.com/2009/05/11/more-practicehelp-on-hcf-lcm-problem-sums/#more-221

[tianzhu]

Hi Essential


Good Morning.

To add to my earlier post, I’ve managed to find some sites which may add to our understanding of HCF.

In this question, students are expected to find the divisor that exactly divides 144,168 and 252 without remainder.

Such a divisor is known as HCF or HCD.

HCF or HCD of two or more numbers is the greatest number that can exactly divide each one of the number. It is covered in greater details in secondary one maths.

You may read more about HCF from these links.

http://www.mathsisfun.com/greatest-common-factor.html

Some useful online tools to calculate HCF.

http://easycalculation.com/hcf.php
http://www.calculatorsoup.com/calculators/math/gcf.php
http://www.free-online-calculator-use.com/greatest-common-factor-calculator.html

Best wishes

[peggy]

Please help with this qtn from school.


In 3 years’ time, Kenneth will be thrice as old as Richie.
Last year, Kenneth was four times as old as Richie.
What will be the sum of their ages next year?

Thank you.

[tianzhu]

peggy:

Please help with this qtn from school.


In 3 years' time, Kenneth will be thrice as old as Richie.
Last year, Kenneth was four times as old as Richie.
What will be the sum of their ages next year?

Thank you.

Hi

I think many students are familiar with this question.

Ming Ming is 6 times as old as her daughter now. Ming Ming will be 4 times as old as her daughter in 4 years’ time. How old is Ming Ming now?

Your question is slightly tweaked from the more familiar version.

The difference in their ages remains the same. Hence, we are talking about “Constant Difference.”

You may use MD. Due to time constraints, I’ll only be providing the pointers for you to draw the MD.

Consider their ages one year ago (last year).
Draw 4 boxes (4 units) to show Kenneth’s age and 1 box (1 unit) to show Richie’s age.

Now, consider their age in 3 years’ time, in this case we need to add a box showing 4 years to the existing unit as we are taking reference from their age one year ago.

Kenneth’s age ------- (4+1 unit) + (4+1 unit) + (4+1 unit)
Richie’s age ------ (4+1 unit)

Compare the MD
3 units ------ 2 units + 8
1 unit -------8

Richie’s age now ------- 8+1 --------9
Kenneth’s age now ------- 9+24 ------33

The question asks for their combined age next year, so the answer is 44.

If you need the MD, please let me know, I'll draw it at a later time.

Best wishes.