Q&A - PSLE Math

Academic support for Primary 6 and PSLE
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ChiefKiasu
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Post by ChiefKiasu » Sat Sep 13, 2008 12:17 am

suiyuan wrote:...1) Kenneth wants to rent a bicycle from Jim’s Bicycle Kiosk. The cost (C) of renting a bicycle for d hours is given by C = $(3d + 5). Find the cost of renting the bicycle if Kenneth wants to cycle for 4 hours. (2 marks)
Cost for 4 hours = $(3*4 +5) = $17
suiyuan wrote:...
2) After 20 minutes in a cross-country race, Alan has run 5/8 of the route while Bernard has covered only 3/8 of the distance. Both run at a uniform average speed each and Bernard runs 60m/min slower than Alan.
(a) Find the total distance of the race.
(b) If Bernard wants to finish at the same time as Alan, by how much should he increase his average speed for the remainder of the race? Express the answer in m/min
(5 marks)
BBBAA---

Let d be the total distance.
Distance travelled by being 60m/min faster after 20min
= (5/8 - 3/8 ) d = 2/8 * d
So 2/8 * d = 20x60 = 1200
=> d = 1200 * 8/2 = 4800

Edit 26 Sep 2008: See lantian's post further down in this thread.
Last edited by ChiefKiasu on Fri Sep 26, 2008 10:09 pm, edited 1 time in total.

lantian
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Post by lantian » Sat Sep 13, 2008 2:20 pm

Hi, Hope this helps

Image
Last edited by lantian on Mon Sep 29, 2008 3:13 pm, edited 1 time in total.

ChiefKiasu
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Post by ChiefKiasu » Sat Sep 13, 2008 2:30 pm

lantian wrote:Hi, Hope this helps...
Ahhh... cunning!

lantian
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Post by lantian » Sat Sep 13, 2008 2:34 pm

Cost for 4 hours = $(3*4 +5) = $17

Hi Chiefkiasu, I think this question if from CHS P6 Prelm 2006

At first glance, the answer is $17.But it's a trick to lead you down a slippery slope.At P6 level, it's difficult to find questions requiring only simple substitution.

If the question is phrased as The cost for renting a bicycle is given by C=(3d+5) where d is the number of hours, then your answer is spot on.

For d hours, the cost is C = $(3d+5)
For 1 hour, the cost is C = $(3d+5)/d
Therefore for 4 hours, the cost C = $4(3d+5)/d
Last edited by lantian on Sat Sep 13, 2008 2:50 pm, edited 1 time in total.

lantian
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Post by lantian » Sat Sep 13, 2008 2:44 pm

ChiefKiasu wrote:
lantian wrote:Hi, Hope this helps...
Ahhh... cunning!
Hi, Chiefkiasu, cunning is not a good word.

I am just a simple minded man who believe that kids should be kids.They should have time to explore their early lives and enjoy their childhoods.They should be no forced feeding to add more misery to their carefree days.My fondest memory of my my childhood days was playing marbles, flying kites and catching spiders.

Best Wishes


ChiefKiasu
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Post by ChiefKiasu » Sat Sep 13, 2008 2:50 pm

lantian wrote:...At first glance, the answer is $17.But it's a trick to lead you down a slippery slope.At P6 level, it's difficult to find questions requiring only simple substitution...
Now that's some trick :P ! Then again, I still maintain that the question is ambiguous.

Is my answer to the 2nd question correct?

ChiefKiasu
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Post by ChiefKiasu » Sat Sep 13, 2008 2:58 pm

lantian wrote:... Hi, Chiefkiasu, cunning is not a good word...
That depends on how it is used. In this case, it is out of respect for the cleverness of whoever thought of that answer. :) No malice intended.
Last edited by ChiefKiasu on Sat Sep 13, 2008 3:00 pm, edited 1 time in total.

lantian
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Post by lantian » Sat Sep 13, 2008 3:00 pm

ChiefKiasu wrote:
lantian wrote:...At first glance, the answer is $17.But it's a trick to lead you down a slippery slope.At P6 level, it's difficult to find questions requiring only simple substitution...
Now that's some trick :P ! Then again, I still maintain that the question is ambiguous.

Is my answer to the 2nd question correct?
Hi Chiefkiasu

I shall try to explain as follows

If it's 3 hours, then the rental is (3*3+5)
For 1 hour, the cost is (3*3+5)/3
For 4 hours, the cost is 4(3*3+5)/3

If it's 5 hours , then the rental is (3*5+5)
For 1 hour, the cost is (3*5+5)/5
For 4 hours, the cost is 4(3*5+5)/5

Working on Q2, not so fast, oldman already.


Best Wishes

lantian
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Post by lantian » Sat Sep 13, 2008 3:09 pm

ChiefKiasu wrote:
lantian wrote:... Hi, Chiefkiasu, cunning is not a good word...
That depends on how it is used. In this case, it is out of respect for the cleverness of whoever thought of that answer. :) No malice intended.

Hi Chiefkiasu

Why bother about little things in life?Tomorrow may never come.

Priskhipo
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Post by Priskhipo » Sat Sep 13, 2008 4:41 pm

Hi KiasuChief,

Refering to Suiyuan's Question on 4 squares and a rectangle within them.
Really have to applaud those members for coming up with creative solution for this question and it is correct in a way because it will not put to test the relative of the sides of smaller square to the biggier square.

But it is not possible for the area of 4 squares to be 80 cm2 if the perimeter of the rectangle is 20 cm.

If someone happen to use strategy of Guess and Check or quadratic equation, he would not be able to find any solution.

See Below:
Solution 1: (Guess and Check)

1 length and 1 breadth = 20 ÷ 2 = 10

L + B = 10 cm

Image

The most squarish rectangle ABCD is 5cm by 5 cm
Area of 4 such squares = 4 x 25 = 100 cm2 (minimum possible total area)

The thinnest rectangle ABCD is 9.9999... cm (round off to 10cm).. x 0.000...001(round off to zero)
= the area of 2 smaller squares is almost 0 cm2
The area of the 2 bigger squares
= 2 x 10 x10 = 200 cm2 (maximum possible total area)

Solution 2: (Using Quadratic Equation to find x)
Breadth = x and Length = (10 – x)
Quadratic Equation = 2xx + 2(10 –x)(10 - x) = 80 (No possible solution)

Sorry, can't superscript. So x multiple by x = xx and so on .
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