## Wednesday, May 30, 2012

### MyPals Circles common errors

It's all being vigilant/ prudent/ wary , to refuse being an "Easy Prey" to the following (non-exhaustive):

• Confusing the formula for C and A (C requires Diameter; whereas A needs the square of the radius) ;
• Mistook radius for diameter or vice versa;
• Using the wrong value of pi for the wrong accasion;
• Missing units in the final answer
• Using the wrong units for the answer (m, cm, m2, cm2):
• "m" instead of "cm" or vice versa
•  Using square unit (cm2) in place of a length unit (cm) for perimeter or vice versa for area.

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Pg 29
Q(e)   --> Missing out the 2 R
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Pg 30
Q3

1st problem
--> 56.55  ??     (actual: 56.54866776)

2nd problem
--> pi x 9  is    "pi x R"  ???!!!    , But   C = pi. D
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Pg 34 (problem with rounding off?)
Q3(b)   5538.96 ~  5539.0    ,    Many with 5538.1 ???

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Pg 36

## Tuesday, May 22, 2012

### Modified question ( P6 percentage, more T-shirts with discount )

A Modified question:

Mr Tan bought some T-shirts for \$425.  If he was given a discount of 16%, he would be able to buy 6 more identical T-shirts for the same amount of money.  What was the original price of each T-shirt?

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In its original form, the question seems unsolvable.  And if only the number "5" is changed to "6", then the question would become quite trivial. :)

## Monday, May 21, 2012

### P6 percentage (fr Chloe p)

Should the "5 more identical T-shirts" be "6" instead? ??

Given:
Diameter of small semi-circle
= 10 cm

Find the area of the shaded parts.
(Take Pi to be 3.14)

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(Take Pi to be 3.14)

Find the difference in area of A and B.

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## Sunday, May 20, 2012

### P6 Percentage (fr bernice)

2) Habri had some 20 cent coins and 50 cent coin. He spent 1/4 of his 20 cent coins and 40% of his 50 cent coins.The value of 20 cent coins left was the same as the value of 50 cent coins left.If the difference between the value of 20 cent coins and the value of 50 cent coins he had at first was \$12,how much did Habri have at first?

### P6 Volume (Fr bernice)

1) A rectangular tank was filled with water flowing from a tap.  At 10 a.m. the tank was empty.   At 1 p.m. the tank was 1/3 filled with water.   At what time would the tank be 7/12 filled with water flowing from the tap?

## Tuesday, May 8, 2012

### P6 Ratio (fr shoe)

And click here for an even easier alternative.  :)  [...similar to Rachel's tutor's solution]

(Note: My earlier answer of 6 sq cm is wrong!  It should be 9 sq cm.  Apologies for any inconvenience caused. :) )

(My Learning Point: the "assigning of variables" should be done in the area where there are physical units added, and not in the area where the units are easily cancelled off. That will defeat the purpose of "assigning of variables" in the first place! )

### P6 Numbers (fr Isaac Tan)

From: Isaac Tan
Date: Sat, May 5, 2012 at 6:13 PM
Subject: math question
To: Chang Cheng Liang <changchengliang@gmail.com>

Hi Mr Chang this is Isaac could you help me with some questions

1.Mr Vroom has some red and blue balloons . If he ties a red balloon with blue balloon, there will be 60 blue balloons left. If he ties 2 red balloons with 3 blue balloons , there will be 50 red balloons left. How many balloons does he have in all?

2..There are some children in the hall . If 1 girl leaves the hall together with 2 boys each time, there will be 8 boys remaining in the hall when all the girls have left. If 1 boy leaves the hall together with 2 girls each time, there will be 107 boys remaining in the hall when all the girls have left.How many children are in the hall if none of them leave?

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For my solutions, click on the respective link below:

### P6 Geometry (PSLE Booklet 2012 p74Q35)

[Psle bklt 2012 p74Q35]