PSLE - New Format for Maths

[leungyc]

pinky88:

[quote]
How is it possible to have the slop same length as the side (the centre line has a \"cut\" indicating same length as the other two lines.

The centre line is from the edge of the square to the other edge. So it's possible.[/quote]If the 3 lines are of the same length, then the angle of the intersecting chord cannot be 90 degree. you can do a mathematical proof that this angle will not be 90 degree, if the 3 lines of the triangle are of same length

[david59]

pinky88:

ilaks:

Hi all,


here is how the image looked like for the geometry question (to best of my child's knowledge)

Not drawn to actual size. Answer was 150

http://www.postimage.org/

This fig. shld be correct. My boy also drew the same image to show me. But he got 120. 150 shld be the correct ans. My hubby work out using the more complex method. Can someone share the soln using the primary level method?

The lower triangle is actually an equaliteral triangle since the 3 sides are equal in length. The angle at the bottom is therefore 60 degrees.

Now, the whole diamond can be cut right through the middle from top to bottom and you get two identical isoceles triangles because the three lines are equal in length. ( remember the diagram is not drawn to scale and accurately)

Each identical triangle has 30 degrees at the bottom. So, the two top angles of each triangle share 150 degrees equally. Therefore each angle is 75 degrees. Thus the two adjacent angles at the top are 75 degrees x 2 equal 150 degrees.
Hope this explanation in words helps. God bless.

[david59]

leungyc:

pinky88:

[quote]
How is it possible to have the slop same length as the side (the centre line has a \"cut\" indicating same length as the other two lines.

The centre line is from the edge of the square to the other edge. So it's possible.

If the 3 lines are of the same length, then the angle of the intersecting chord cannot be 90 degree. you can do a mathematical proof that this angle will not be 90 degree, if the 3 lines of the triangle are of same length[/quote]The centre line which is equal to the two slanted lines is measured from the top to the bottom of the diamond. I think some students misunderstand the symbol to mean from the point of the cross section to the bottom of the diamond which would certainly make it impossible to draw the diagram.

[Joy]

Hi


Can i check with you , is there any other information given besides the diagram?thanks

rgds

kohjl:

ilaks:

Hi all,

here is how the image looked like for the geometry question (to best of my child's knowledge)

Not drawn to actual size. Answer was 150

http://www.postimage.org/

Thanks for sharing this question. Were any other dimensions given, like the sides of the rectangle, etc?

[CrazyDad]

I think any number between 90 degree and 179 degree will be considered correct. By drawing a semi circle, draw any two lines from the centre of the circle to the edge of the circle. Then draw another line right in the middle of the two. Any diagram drawn under the above condition fits the question, unless something is missing. So I believe fee point will be awarded to all students.



or just day dreaming :idea:

[Joy]

I also think so cos the info is inadequate.

CrazyDad:

I think any number between 90 degree and 179 degree will be considered correct. By drawing a semi circle, draw any two lines from the centre of the circle to the edge of the circle. Then draw another line right in the middle of the two. Any diagram drawn under the above condition fits the question, unless something is missing. So I believe fee point will be awarded to all students.


or just day dreaming :idea:

[turquoise]

The answer is 150 deg. The easiest way to get the answer is via the equilateral triangle and isosceles triangle method. Several posters have already shown how to derive the answer.


If still in doubt, draw the figure on a piece of paper, making sure you have a square, and the three lines are of the same length. Measure the angle. It’s 150 deg.

[chochipkooky]

Does anyone know whether it was clearly shown that the 4 sides were of equal length thus making it a square? If not, I agree with CrazyDad. Information inadequate.

[turquoise]

chochipkooky:

Does anyone know whether it was clearly shown that the 4 sides were of equal length thus making it a square? If not, I agree with CrazyDad. Information inadequate.

It's stated in the question.

[James Ang]

chochipkooky:

Does anyone know whether it was clearly shown that the 4 sides were of equal length thus making it a square? If not, I agree with CrazyDad. Information inadequate.

Yes, it is a square and the information is provided that it is a square as my students have told me. That means all the 3 equal lines are the radii of the arc (incomplete circle) and that makes all the 3 lines (length of square) and all the 3 radii equal and thus the equilateral triangle.