Today I’d like to post up some samples of common mistakes made by my students. I have compiled 5 examples here from their actual exam papers and made some notes in red about their mistakes.

I’ve also written the correct solution in red.

Drop me a comment or mail if you still have trouble understanding these examples.

**Example 1**

1) You cannot multiply 2 and 16 because the number 16 has power to it.

2) This student got the concept right which is to make the base number same on both sides.

**Example 2**

1) Here, the student made the mistake of adding Log 2 to the number 8. This makes it equals to 3 instead of 8 which is wrong.

2) What should be done is to leave the number 8, move the number 2 to RHS, and keep the log x on LHS

3) Observe my workings, in the 1st line, I multiplied 2 on both sides of equation to get rid of the fraction 2.

__Example 3__

1) Here’s a very very common mistake. Students often try to expand Log as if it’s an algebraic equation. It is NOT.

__Example 4__

1) Here are 2 answers by 2 different students on the Chapter Linear Law in Form 5 Add Maths. They are required to convert a non-linear equation to linear equation and very often, Log has to be used. So if your Log is terrible, then you’ll most likely struggle with this chapter.

2) Also note that this Chap – Linear Law is a very very very common question in Paper 2, Section B. Yes – you can choose not to do this, but let me assure you that this question is very easy to get 10 full marks, compared with Differentiation of Integration or Circles.

3) The top paper is wrong – the student made the same mistake as the one in example 3. They expanded the bracket as if it’s a normal Algebraic equation. In fact, in this paper, there are few other mistakes that I did not point out. See if you can spot them!

4) The paper in the bottom is by another student, and it’s correct.

__Example 5__

1) I’ve created a video to answer this type of indices question. View it here.

Feel free to drop me any questions that you need help with. What I suggest is you snap a pic of the question, or if you have a scanner, scan it in and mail me.

I will do the answers and post them up here. Or I may even make a video out of it

Question : Simplify 5 exp(x-2) + 2(5 exp(x)).

The answer is (52/25) 5 exp(x) or 52( 5 exp (x-2)) ?

Hi Matt,

I believe the answer is (51/25) 5 exp x or 51 (5 exp (x-2)). Not 52.

Anyway, to answer your question – both answers are correct. The final simplified answer should be 51 (5 exp (x-2)). You should always complete all the indices whenever possible, ie when they are same base.

rubbish…

i wanna see how smart u are

(my school form5 past year paper also related to Arithmetic and geometric progression)

Given that a, b, c are GP.

Prove that Lg a, Lg b and Lg c are AP.

(Lg means Log 10)

when u got the answer, u can post at here then email to jiaminglee@yahoo.com

My dear boy – I’m assuming you’re a boy and that you’re still a SPM student and not an adult making trouble here…

There’s such a thing called respect in this world.. and the fact that I’m a teacher and you’re a student, you should know better than to refer to something I make with the intention to help students .. to refer to something like that as “rubbish”.

Also… it is indeed very rude to challenge a teacher. “I wanna see how smart you are” is cocky and egoistic. Even my smartest student who always get 100% for Add Math never say that to his teachers.

Furthermore, it is funny to see that the question you posted is actually something so easy that I can get my student to answer it for you.

I’ll answer it here… don’t need to make video.

But please remember this : I’m not taking your challenge. (so don’t bother putting up more challenges. this is education, not wrestling or boxing competition)

I just think this is a very simple question but there are students like you who doesn’t know how to answer, so as a teacher, I want to help them.

Lg a, Lg b, Lg c is AP. Therefore they have common difference, d

Lg b – Lg a = Lg c – Lg b

Lg (b/a) = Lg (c/b)

b/a = c/b

a,b,c is GP, therefore they have common ratio.

b/a = c/b

Proven.

Hello teacher!

May i ask whether that my solution is correct for the question posted by Mingz.

Given that a, b, c are GP.

Prove that Lg a, Lg b and Lg c are AP.

Solution:

since a,b,c —>G.P

b/a=c/b

lg (b/a)=lg (c/b)

lg b- lg a=lg c-lg b

2lg b=lg a+lg c

lg b=(lg a+lg c)/2

which (lg a+lg c)/2 is the arithmetic mean for the sequence lg a, lg b and lg c. Hence, proven that lg a, lg b and lg c is an A.P.

It’s surely correct!

teacher, i think mingz created steam. he’s not right and ya, the question really not a challenge. mingz, only ppl who are less wise will think he knows more. wiser ppl knows they have more that they dunno. digest that.

teacher, yr method proved it’s G.P but mingz question is asking to prove A.P from G.P relation. so, isn’t crazyone working more appropriate? or it’s ok to show reverse?

teacher,i dont understand the question no 8. i wanna ask why 2(2^4x-3)become 2^1+4x-12 .

eh, sorry. no 6 a