Q&A - PSLE Math

[corneyAmber]

pardon me if my brain thinks too simply...



i used the first sequence as (7+3) + 7 + 7 + 7........... so 10 + (7*?)

and second as (9-6) + 9 + 9 + 9 .................. so 3 + (9*?)

10 + (7*?) = 3 + (9*?)

7 + (7* ?) = 9*?

can do?

[suiyuan]

Thank you for your help.



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[lizawa]

Let AD be x cm

Let AB be y cm
\t
Perimeter of ABCD = 20cm
so, x+y = 20/2 = 10 cm

Area of big square = y2
Area of small square = x2

Area of 4 sqaures = 80 square cm
So area of 1 big + 1 small = 40 square cm

x2 + y2 = 40

x + y = 10
(x+y)(x+y) = 100
x2 + y2 + 2xy = 100
40 + 2xy = 100
2xy = 60
xy = 30

Area of shaded rectangle = xy = 30 square cm.

Is the answer correct ?

[suiyuan]

Hi lizawa


Thank You.
I am sorry, no answer was given.

[suiyuan]

Thank You for your time.


1) Kenneth wants to rent a bicycle from Jim’s Bicycle Kiosk. The cost 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)


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)

[ChiefKiasu]

lizawa:

...

(x+y)(x+y) = 100
x2 + y2 + 2xy = 100
40 + 2xy = 100
2xy = 60
xy = 30

Area of shaded rectangle = xy = 30 square cm.

Is the answer correct ?

*clap* *clap* That is the right answer. However, are children in P6 taught how to do an expansion of (x+y)^2 ? Without that step, it is impossible to solve the equation.

[ChiefKiasu]

suiyuan:

...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:

...
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.

[lantian]

Hi, Hope this helps


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[ChiefKiasu]

lantian:

Hi, Hope this helps...

Ahhh... cunning!

[lantian]

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