Saturday, November 24, 2007

If everybody gets the same answer, it has to be right. Is it ?

I was on leave yesterday and happened to have time to go through my son's final mathematics examination paper (2nd Semester Assessment in 2007, Primary 5) . He scored 86 out of 100 and I can see he improved quite a lot. Normally I will go through his assessments and focused on those that are incorrect. One of the questions in that paper got my attention. It seemed everybody is correct, however in reality it is not. My son was telling me that most of the students got the 'correct answer' which is 110. So, the question is: Is my son not careful enough to measure it correctly and that lead him to an incorrect answer ? Let's do the CIS work.

The question is:
Draw a triangle EFG in which EF=7cm, angle EFG=30 degree and FG=10cm. Measure angle FEG.
The student supposed to use ruler and protractor to accomplish the task. Below showed the examine question with my son's working on the left and the 'model answer' in green copied from the whiteboard. Obviously the red color cross is marked by the teacher. My son was telling me that any answer between 109 and 110 is considered to be correct, ie. with 1 degree tolerance. Fair enough.

So I took the ruler and protractor to work it out on my own to see whether I can get the answer within the same tolerance level. I got the same answer as my son. Wait a minute, this can't be right 'cos I took extreme precaution to ensure I measure extactly 7cm, 10cm and 30 degree.

Okay, why not use trigonometry to work out the exact answer. See below for proof.

Hey, the correct answer should be 108.37. If we were to round to the nearest degree, it should be 108. If we were to based on the tolerance level given by the teacher, the answer should be between 107 and 109. Definitely 110 is not the correct answer.

I even used Geogebra to verify it.



Blogger Indian Stallion said...

So how, did you let the teacher know?

1:01 PM  
Blogger chihungchan said...

I will email the person-in-charge for Maths. If no response, I will follow up with Vice-Principal, Principal, MOE, ....
BTW, read my next blog to know why I wanted to blog about this.

4:25 PM  

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