{"id":2501,"date":"2010-03-01T10:14:17","date_gmt":"2010-03-01T18:14:17","guid":{"rendered":"https:\/\/gmatclub.com\/blog\/?p=2501"},"modified":"2010-12-15T07:14:58","modified_gmt":"2010-12-15T15:14:58","slug":"knewton-gmat-prep-tip-common-sense-on-data-sufficiency","status":"publish","type":"post","link":"https:\/\/gmatclub.com\/blog\/knewton-gmat-prep-tip-common-sense-on-data-sufficiency\/","title":{"rendered":"Knewton GMAT Prep Tip: Common Sense on Data Sufficiency"},"content":{"rendered":"

Rich Zwelling is one of Knewton\u2019s top GMAT prep<\/a> teachers, and he loves thinking of ways to crack the Data Sufficiency section<\/em>.<\/p>\n

\u2013<\/p>\n

Data Sufficiency questions are often difficult to get used to, because they require an adjustment in your approach to math problems.\u00a0 When you went through math classes in high school, the end goal was always \u201cFind the value of x\u201d or \u201cFind the area of this circle.\u201d\u00a0 You were asked to give hard responses to these questions, and nothing mattered more than finding a definite value.<\/p>\n

With Data Sufficiency, answering the question does not matter as much as the ability to answer the question<\/em>.\u00a0 You are not primarily concerned with the final answer, but rather whether you have enough information to get you to that answer.\u00a0 For example, if you\u2019re asked to find the value of x, and a statement tells you that 300x + 257 = 1345, you know that this statement is sufficient, because you can perform arithmetic on that equation to isolate x.\u00a0 Are you going to perform it?\u00a0 No, because it\u2019s too complicated and you don\u2019t need to!\u00a0 All you\u2019re concerned with is whether you can<\/em> find the answer.<\/p>\n

It might strike you as odd, but because of this principle, you can tackle some supposedly difficult DS questions without writing down a single equation or calculation!\u00a0 Sounds too good to be true, but in actuality, it makes a lot of sense.\u00a0 Remember, in business school you\u2019ll be given data in case studies, and you\u2019ll be expected to determine relatively quickly what information is relevant.\u00a0 DS questions are perfect for testing this ability because you have to look at the information given to you and cut to the heart of what is most important about that information.<\/p>\n

As an example, let\u2019s look at this rather wordy DS problem:<\/p>\n

Effie bought an armchair and a coffee table at an auction and sold both items at her store.\u00a0 Her gross profit from the purchase and sale of the armchair was what percent greater than her gross profit from the purchase and sale of the coffee table?<\/em><\/p>\n

(1)\u00a0 Effie paid 10 percent more for the armchair than for the coffee table.<\/em><\/p>\n

(2)\u00a0 Effie sold the armchair for 20 percent more than she sold the coffee table.<\/em><\/p>\n

First, let\u2019s approach this algebraically to show how cumbersome it ends up being:<\/p>\n

In general, Gross Profit (P) is the Selling Price (S) minus the Buying Price (B):<\/p>\n

P = S \u2013 B<\/p>\n

We want to know what percent greater the profit of the armchair (P_armchair) is than the profit of the coffeetable (P_coffeetable).\u00a0 If we represent the missing percent as x, then the equation would be<\/p>\n

P_coffeetable*(1 + x\/100) = P_armchair<\/p>\n

Rearranging, we would get:<\/p>\n

x = 100*(P_armchair \/ P_coffeetable \u2013 1)<\/p>\n

We know that P = S \u2013 B, so we can substitute:<\/p>\n

x = 100*[(S_armchair - B_armchair\/ (S_coffeetable - S_coffeetable) - 1]<\/p>\n

Confused yet??\u00a0 I sure am!!<\/p>\n

But try to look at things from a sufficiency point of view.\u00a0 Notice that you need absolute values for the gross profits in order to solve for x.\u00a0 You could also find the ratio between the two gross profits.<\/p>\n

Now that we\u2019ve seen how ugly this looks when all the algebra is written out, let\u2019s take a more common-sense approach.<\/p>\n

The prompt:<\/p>\n

Effie bought an armchair and a coffee table at an auction and sold both items at her store.\u00a0 Her gross profit from the purchase and sale of the armchair was what percent greater than her gross profit from the purchase and sale of the coffee table?<\/em><\/p>\n

What we need in order to determine sufficiency:<\/p>\n

In essence, this question asks you to compare the values of two profits.\u00a0 You need the value of each profit OR the ratio between the two profits.\u00a0 Notice that you can figure out what information you will need without writing down a single number or algebraic expression.<\/p>\n

What each statement tells us:<\/p>\n

(1)\u00a0 Effie paid 10 percent more for the armchair than for the coffee table.<\/em><\/p>\n

Without writing any math, you can deduce that this is insufficient, because buying prices are mentioned, but no selling prices.\u00a0 And with no selling prices, we certainly can\u2019t determine anything about profit.<\/p>\n

(2)\u00a0 Effie sold the armchair for 20 percent more than she sold the coffee table.<\/em><\/p>\n

Now, we\u2019ve got information about selling prices, but nothing about buying prices.\u00a0 Again, Insufficient because there is no way to determine profits.<\/p>\n

So far, nothing too difficult.\u00a0 It\u2019s pretty simple to narrow this down to C and E.\u00a0 But how do we determine whether the statements together are sufficient?<\/p>\n

You could test numbers here, but really all you need to do is realize that the statements only give you percentages to work with.\u00a0 For the sake of illustration, let\u2019s pick numbers to see what this means:<\/p>\n

According to Statement 1, Effie could have spent $100 on the coffee table and $110 on the armchair, or it could have been $10 on the coffee table and $11 on the armchair.\u00a0 (Unlikely prices, maybe, but remember, the real world doesn\u2019t apply here!)\u00a0 There are infinite possibilities for what the buying prices could have been.<\/p>\n

Likewise, Statement 2 tells us that Effie could have sold the coffee table for $100 and the armchair for $120.\u00a0 Or it could have been $10 for the coffee table, $12 for the armchair.<\/p>\n

You\u2019ll notice that because the absolute numbers for selling and buying prices vary so much, so too do the gross profits!\u00a0 And if the gross profits can fluctuate that drastically, there is no way on Earth you can nail down one specific percentage increase from one profit to the next!<\/p>\n

And thus, without writing a single equation, you can determine that the answer must be E.<\/p>\n

It\u2019s very very tricky to get your mind to think this way, especially since you\u2019ve been trained all your life to hack away at a problem until you come up with a definite answer.\u00a0 But it is absolutely imperative that you begin to look past the math of DS questions and ask yourself what information is necessary to solve the problem<\/em>.<\/p>\n

Click here to learn more about Knewton's GMAT prep course<\/a> or find more helpful articles on their GMAT blog<\/a>.<\/div>\n","protected":false},"excerpt":{"rendered":"

Rich Zwelling is one of Knewton\u2019s top GMAT prep teachers, and he loves thinking of ways to crack the Data Sufficiency section. \u2013 Data Sufficiency questions are often difficult to…<\/p>\n","protected":false},"author":104,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,243],"tags":[384,381,346],"class_list":["post-2501","post","type-post","status-publish","format-standard","hentry","category-gmat","category-blog","tag-data-sufficiency","tag-gmat-math","tag-knewton","entry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/posts\/2501","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/users\/104"}],"replies":[{"embeddable":true,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/comments?post=2501"}],"version-history":[{"count":3,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/posts\/2501\/revisions"}],"predecessor-version":[{"id":5566,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/posts\/2501\/revisions\/5566"}],"wp:attachment":[{"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/media?parent=2501"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/categories?post=2501"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gmatclub.com\/blog\/wp-json\/wp\/v2\/tags?post=2501"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}