Disturbed.

RC accuracy remains intact with 6/6 answers right.

PS - need to review Number Properties (esp Remainders).

DS - accuracy fell massively - 4/10 wrong.

CR - got 2/10 wrong.

Overall, getting better. Feel better. But, need to review old concepts. AND not be disturbed while doing my questions!!!

Also, got access to BTG account as a winner of BTG 100k Challenge! :)

Will also write a review on new & improved BTG premium questions by end of this week!

Stay tuned fellow gmatters!

Remainder of today's CPs.

This is the link to Remainder questions. Sriharimurthy's explanations are really good. Good questions to repeat at some later stage! Have understood them for the time being. Should probably note down what I've understood here or elsewhere, so as to not go through the whole thread all over again. Phew. I'm tired now, have solved and understood quite a few challenging questions today!

To Do:
Combinatorics tutorial from MGMAT
Kaplan questions - P&C, Probability, and all the other topics.

CP #15

From GMATClub Math Book Remainders:

If s and t are positive integer such that s/t=64.12, which of the following could be the remainder when s is divided by t?
(A) 2
(B) 4
(C) 8
(D) 20
(E) 45

OA: E

Using the concept,

If you take the decimal portion of the resulting number when you divide by "n", and multiply it to "n", you will get the remainder.
Eg. 8/5 = 1.6
0.6*5 = 3 = remainder

In our question,
0.12*t = R(remainder)
Since R has to be an integer, it must be a multiple of 0.12.
To make the calculation simpler, we multiply both sides by 100.
12*t = 100R

Now, put the value of different Rs in the equation and find which one is perfectly divisible by 12.

i.e. which one of

(A) 200
(B) 400
(C) 800
(D) 2000
(E) 4500

is perfectly divisible by 12 or 3*4.
All are divisible by 4, since they end in 00s.
Only (E) is divisible by 3 also (4+5=9).

Answer is therefore, (E) 45.

The Mystery of the Divisor Addition to the Negative Remainder

I have a doubt regarding the formula used for Remainders in GMATClub's Math Book: see Point #6, Eg. #2.

Q. What is the remainder of (20*27) when it is divided by 25?

Note: Rof = remainder of

A. The formula I used is: Rof xy/n = Rof {Rof[(x-n)/n] * Rof[(y-n)/n]} / n

Therefore,  Rof 20*27/25 = Rof {Rof[(20-25)/25] * Rof[(27-25)/25]} / 25
= Rof {Rof[(-5)/25] * Rof[2/25]} / 25
= Rof [(-5 * 2) / 25]
= Rof [(-10) / 25]
= (-10)

But, since the remainder is negative, we add n to it to give us the remainder.
Therefore, Rof 20*27/25 = -10 + n = -10 + 25 = 15.

Why did we add n to the negative remainder?

1 hr to go to office 20 kms away, 1 hr 15 mins to come back. On an avg, how much time do I waste everyday?

Finished Distance, Speed & Time from a GMATClub post. The tabular representation method is brilliant. It saved me a lot of time, since I don't have to keep writing the different forms of the formula S=D/T for every component of the question. Am definitely using the table form from now on! :-)

Also went through the post on Work problems. Didn't require much effort since my concepts are pretty clear. The only issue I have here is the time I take to solve a question, if I only rely on my concept. I will need to practice a lot of Work problems, and probably revisit my TIME notes for shortcuts. Buit I will get back to this post my diagnostic test, as the diagnostic test is untimed. Plus, there is only a limit to how much I can do in every topic over the next 2 days. Yup, probably giving the test on Saturday. Should revise everything on Friday. Phew...

Update on P&C: went through most of the solved examples in RS Aggarwal, need to wrap up Combinations with the last few questions from the book. Once this is done, need to go back to the GMATClub Math book chapter on Probability and try solving those examples I was having trouble with.

As for Remainders, still need to speak to that friend regarding the questions from the link I did not understand.

The Remainder of the previous post.

Before I forget, I also went through a post on Remainders. The formulae are easy, but when I tried solving the last question, I couldn't understand the reasoning. Also, there was a link to other questions - I had a problem grasping the reasoning there too. Need to sit down with my friend and understand all these concepts, before I can consider remainder theory finished.