Q&A - PSLE Math

[Michaelia0816]

Tianzhu, I had already give u the website to go to the picture to see already, how? Can solve? Do you know what it is referring to actually?

[elenatay]

Hi everyone,

This is my first time posting here. Can anyone help to solve this?

Jim bought some chocolates and gave half of it to Ken. Ken bought some sweets and gave half of it to Jim. Jim ate 12 sweets and Ken ate 18 chocolates. The ratio of Jim’s sweets to chocolates became 1:7 and the ratio of Ken’s sweets to chocolates became 1:4. How many sweets did Ken buy?

Thank you.

[Michaelia0816]

elenatay:

Hi everyone,

This is my first time posting here. Can anyone help to solve this?

Jim bought some chocolates and gave half of it to Ken. Ken bought some sweets and gave half of it to Jim. Jim ate 12 sweets and Ken ate 18 chocolates. The ratio of Jim's sweets to chocolates became 1:7 and the ratio of Ken's sweets to chocolates became 1:4. How many sweets did Ken buy?

Thank you.

Hi, it would be faster to give you the answer here than going to another pages, I have taken their answer for their posts,

sorry for the copyright, i think it alright as i am doing so for helping.

Suggested solutions
Draw a model to show \"after eating\" scenario,

Ratio of Jim's sweets to chocolate (1:7)
Sweets []
Chocos [][][][][][][]

Ratio of Ken's sweets to chocolate (1:4)
Sweets [] +12 (+12 refers to the sweets eaten by Jim)
Chocos [][][][] (+12x4) - x 4 times

Both amount of Chocolates are the same,so
(7-4) units = (12x4) + 18 (18 chocolates were eaten by Ken)
3 units = 66
1 unit = 22

Amount of sweets bought by Ken->(unit +12)x2=(22+12) x 2 =68

Or use algebra which is easier.

Assume that sweets that Ken bought was S and chocolates that bought by Jim was C.

Before both of them ate, they had:
Ken -> 0.5C + 0.5S
Jim -> 0.5C + 0.5S
as each of them gave 1/2 to each other.

Jim ate 12 sweets and the ratio of Jim's sweets to chocolates became 1:7.
(0.5S-12)/0.5C = 1/7
3.5S-84=0.5C

Ken ate 18 chocolates and the ratio of Ken's sweets to chocolates became 1:4.
0.5S/(0.5C-18 ) = 1/4
(0.5C-18 ) / 0.5S = 4
0.5C-18 = 2S

3.5S-84-18=2S
3.5S-2S = 84+18
1.5S = 102
S = 102/1.5 = 68

Amount of sweets bought by Ken-> 68

[Michaelia0816]

and also welcome elenatay to here!

[Michaelia0816]

tianzhu:

Michaelia0816:

Tianzhu, help!


The figure below is formed by stacking 4 cardboard of equilateral triangles one on top of another. The triangles have sides 3cm,4cm,5cm and 6cm. The 6cm piece is triangle ABC. It is placed at he bottom of the stack followed by the 5cm piece, then the 4cm piece and the 3cm piece is right on top. What faction of the triangle ABC has only 2 layers of cardboard?

I am not sure of the phrase highlighted in red! Do give step by step answer!

Hi

Please post the figure.

Best wishes

REMINDER!!



The picture is could be found at this website,pic.twitter.com/rg7SCB5F

[tianzhu]

Michaelia0816:

REMINDER!!

The picture is could be found at this website,pic.twitter.com/rg7SCB5F

Hi girl

Wow, the first reminder I received in KSP.

Better answer, if not later kena “yellow card”.

Unfortunately, the link no longer works.

I saw the question briefly this morning.

Best wishes

[Ah Mao]

Hi all,

by looking at the picture at:
pic.twitter.com/rg7SCB5F

Lets called the smallest triangle A, 2nd one called B, 3rd - C and the triangle at the bottom (the biggest one called D).

Michaelia0816: only 2 layers means the part where there is only layer C and D, ie the one in the picture where the student put the \"4cm\".

Analysis:
Cos the part where the student put 5cm\" is only the triangle D cos it is the bottom layer and triangle C didnt touch that portion.

the part where the student label \"3cm\" is the part where triangle B,C,D are the 3 layers.

the part smallest triangle where there are no labelling on the picture is 4 layers.

hope above can make you understand the qn

[Ah Mao]

As for how to do,

first student will know triangle = 0.5 x base at height.
base is given. slant sides which is equ tri so they know is the same number, but vert h is not given.

so this is actually a proportional qn taught in sec, but cat high paper like to ask this qn anyway.

Understanding wise:
if triangle A is 3cm base.
triangle B is 4cm base.

then their area will be (3/4)^2
ie triangle A will be 9units cm2
triangle B will be 16units cm2

the above is ok to use cos they didnt ask for actual AREA but ask for fraction, which is proportion qn.

to find the part labelled \"4cm\" (ie the 2 layers), find:

STEPS by STEPS answers:
tri C -> 5 x 5 = 25 units cm2
tri B -> 4 x 4 = 16 units cm2
so the 2 layers = 25-16 = 9units cm2

so the biggest tri is -> 6x6 = 36units cm2

so ans is 9/36 = 1/4

[YumYum]

Hi,


Need help with this;

Raju drove at a constant speed from his house to town B. On his way, he passed Town A. At 9.20 a.m he was 383 KM from Town B and 205 KM from Town A. At 12.50 pm, he stopped at a petrol kiosk which was midway between Town A and Town B. At what speed did Raju drive before he came to the petrol kiosk?

Thanks

[Ah Mao]

Michaelia0816: need to emphasize the 5x5, 3x3 working is correct. BUT cannot write 9cm2, must be 9units cm2. cos the 3 we use for vertical height is not the ACTUAL measurement, is a proportion


YumYum
hard to understand without diagram:
try to draw a time line on a piece of paper?

Analysis:
Raju drove at a constant speed from his house to town B.

draw:
H -------------------------------B

On his way, he passed Town A.

draw:
H -------------------A ------------B (on the same diagram)


At 9.20 a.m he was 383 KM from Town B and 205 KM from Town A.

draw:
H --------------920am----------A ---------------------B
205km 383-205=178km

At 12.50 pm, he stopped at a petrol kiosk which was midway between Town A and Town B.

draw:
H --------------920am----------A ---------------------B
205km 178km
midway means 178 / 2 = 89km

draw:
H --------------920am----------A ----------P-----------B
205km 89km 89km


At what speed did Raju drive before he came to the petrol kiosk?
draw:
H --------------920am----------A ----------1250pm: P-----------B
205km 89km 89km


time taken: 920am to 1250pm is 3.5hours.

from 920am to 1250pm he drive from diagram:
205 + 89 = 294km

so speed = D/T
= 294km/3.5h
= 84km/h