Ok, so basically since yesterday I am mostly doing the exercises on official book to get practice. With such little time to learn I feel the best investment of time these last days is just to keep my mind engaged. Solving problems and analyzing if I make mistakes!
Important learning. There is a kind of question that always gets me or slows me down. These involve basically saying… “A stand sells apples at 0.7 and bananas at 0.5, if sold 6.3 how many apples and bananas did the customer purchase? These always slow me down because an equation doesn’t give u the answer right away and you need to basically do some plugging and trial and error. Luckily this time I followed the right process and got it right in 1:54 sec… but I wonder if I can be more efficient in these problems. One big learning of this kind of problem is to already know from beginning that an equation on its own won’t solve it. This already saves you a lot of time going the wrong way.
For this particular one one way is to realize that 63 contains 7 as a factor… 7*3*3. And by the title we know this equation holds 0.7a + 0.5b = 6.3 hence this equation holds 7a + 5b = 63 Hence this holds 5b = 7(9-a) hence we know for sure… that if a and b are integers… (9-a) will have to be a multiple of 5, and b will have to be a multiple of 7. So we know b can be 0, 35 or 70 etc… which clearly tells us b is 4. Now, this approach is actually good to know as a concept especially when numbers given are pretty big, because then one needs to really think about factors etc… but at the end of the day, a table with all multiples of each value, can also shed light and avoid mistakes. I feel it is important to write the table also and keep both approaches in mind. This kind of question anyway (especially in Data Sufficiency) are some of the longest cases. So I might as well take it as a guessing question.
- The question above, questions about work, questions about ratios I am slow… but I am a bti stronger now, and porb wont take more than 2:20 to solve. I think it’s an ok trade off. I don’t wanna learn too many formulas with such little time. So anyway good to keep it in mind though.
- Another learning regarding averages. Hmm… question I got right by plugging when seeing I couldn’t find a quick solution algebraically, and got it right in 2:49s so totally insufficient. Main issue was not realizing a clear path that could have taken. Queastion is below:
Basically a much quicker path would be to realize that sum of total scores is 10x and that includes the sum (or contribution) of all students! And we also know the sum of the 5 students, which is 40. Hence the sum of remaining students exluding those 5 is 10x – 40, and this divided by 5 is the average score of those. Hence 2x – 8.
It is very important to learn approaches like above… because this is precisely what GMAT tests. It’s not about knowing what average is… its about knowing what the quickest method to get to an answer in a case like above is.
- Learning in 2 matrix, to know when sufficient and when not. If I want to know total, then I must know the sum of extreme right cells or extreme bottom. Hence if low right quadrant missing but I have everything else, I still can’t know total-
- Another learning point is to not start messing up with an equation in a DS title wihtout first looking at the answers. There are many ways one can rearrange the equation. The whole point is to rearrange it in a way that it will help you compare it with the given statements.