Comments on: One Cumulative Frequency Curve To Rule Them All

By: The Day of Mathematical Armageddon & The 2008 O-Level AMaths Solutions Scribbled In Miss Loi’s Notorious Handwriting | Jφss Sticks | Diary of a Private O Level Maths Tutor in Singapore

Mon, 27 Oct 2008 06:58:29 +0000

[...] Loi managed an ironic smile. At least there won’t be too much moderation this time round. I only lose marks at the similarity one. Cause I anyhow give reason. But maybe [...]

By: BP stabbed

BP stabbed — Sat, 27 Oct 2007 23:31:49 +0000

Seems like the "war" has begun. best wishes to all those participating.
*Fighting!*

By: Miss Loi

Miss Loi — Sat, 27 Oct 2007 19:39:33 +0000

Prodigy, Miss Loi has marked your answers. Please pay particular attention to Parts 4 and 5.

A little scary that the values in this question seem a tad too 'realistic' eh?

By: Miss Loi

Miss Loi — Sat, 27 Oct 2007 19:37:08 +0000

123, well it's the sign of the times. Gone are the carefree days when you only have to compete with your cousin, or your mother's friend's daughter, or your uncle's friend's friend's son etc. etc.

By: Prodigy

Prodigy — Sat, 27 Oct 2007 10:44:40 +0000

[1] 60

That's right. The median is the value of the middle term of the set of data arranged in increasing order. In this case, the middle term is the 60th out of the 120 students, and it's corresponding marks for Paper 2 is 60.

[2] 72-45 = 27

Yes if you refer to the little diagram Miss Loi has drawn up. The interquartile rage is Q3-Q1

Q3
= Marks at 75% of 120
= Marks at 90
≅ 72

Q1
= Marks at 25% of 120
= Marks at 30
≈ 45

So Q3-Q1 ≈ 72-45 ≈ 27

Again Miss Loi would like to stress that we're looking for the values i.e. those on the horizontal axis corresponding to the data on the vertical axis. Many students make the careless of mistake of reading directly off the vertical axis.

[3] 120-85 = 35

Righto! The keyword here is more than 70 marks, which includes all who scored between 70-100. From the Paper 2 graph you get the lower limit of 85 students (who scored 70) and the upper limit of 120 students (who scored 100). So the number of students in this range is 120-85 = 35 students.

[4] From the graph, pass mark would be 65.

You got pwned here! A good way to check is if you set 65 as the passing mark, and if you look at the graph again, 0-72 students scored between 0-65 marks. Will you PASS your exam if you score zero? No way! So you actually FAILED 60% of the students with your cutoff of 65!

Will you PASS if you score 100? Of course. So you should instead look at the top 60% of the frequency axis in the graph, i.e. 60% of 120 starting from 120 (instead of starting from 0). Therefore you should be getting the passing mark from 40% of 120 = 48 ⇒ passing mark is around 55.

BE VERY CAREFUL IN THESE KIND OF QUESTIONS! Many students got caught out here!

[5] From the graph, mark= 83 {approx}

Let's check again ... if you set 83 as your distinction mark, you'll get 114 (95%) students scoring 0-83, which means they failed to attain the distinction grade, which means only 5% get it. This time you correctly used the top 5% so you're right!

Actually part 5 requires the same method to solve as part 4, and your 'instincts' served you well when it's the top 5%. But things don't look so obvious when it's the top 60% ;)

Paper 1 is more difficult, as median mark of Paper 1 is lower than the median mark of Paper 2.

Absolutely! Those who're still not sure let's chant the mantra together!

Higher median = easier paper.
Lower median = more difficult paper.

Repeat this 20x before you go to bed and always remember that for medians and quartiles we're interested in the corresponding values on the horizontal axis. Don't make this careless mistake in your exam!

~~~~~~~~~~~~~~

By: 123

123 — Sat, 27 Oct 2007 08:28:52 +0000

Lol, Haha, Foreign cyborg mercenaries....i agree

By: Miss Loi

Miss Loi — Wed, 24 Oct 2007 16:37:33 +0000

Welcome to Jφss Sticks Karen!

As mentioned earlier, no point worrying about things beyond your control okay?

Rumours are now flying all over the place as to what's the A1 cut-off.

But the perennial question remains: who assigns your grades? Is it Cambridge or SEAB aka the War Council? If it's Cambridge then the pool of people is more spread out but if it's SEAB then you're probably competing with a pool of people at the higher-end, namely Singaporeans and our foreign 'talents'.

Miss Loi has heard from somewhere that gradings were being determined through some 'collaborative meetings' between Cambridge and SEAB reps. And if that's true, then it's highly probable we're looking at the latter case due to SEAB's involvement.

In any case, Miss Loi isn't 100% sure on this and is still waiting for anyone in the know to confirm this.

But then again it's always good to aim high

By: Karen

Karen — Wed, 24 Oct 2007 13:56:17 +0000

I was told that according to Cambridge report, the A1 cut-off for A Maths would never exceed 80, because they still need to take into consideration the "less able". Ah well I'm just worried about losing my A1 because I was so terribly careless.

By: Miss Loi

Miss Loi — Wed, 24 Oct 2007 11:56:53 +0000

Shihui, no point worrying about things beyond your control. But do focus on things that are within your control i.e. go study your Geography!

By: shihui

shihui — Wed, 24 Oct 2007 09:25:50 +0000

huh! then top how many percent will get distinctions! what if everyone get 90 plus then the A1 will be 90 plus! oh dear!