Can Someone Please Help Me( Division Strategy)

Question

I am looking for a strategy that will help me calculate 138/.82 fast. I am having the hardest time learning how to divide decimals fast. Thanks

fluke · Answer

\frac{138}{.82}=\frac{138}{82*10^{-2}}=\frac{138}{82}*10^2=\frac{69}{41}*100

Multiply numerator & denominator by 5 as 40*5=200

\frac{69*5}{41*5}*100=\frac{69*5}{200}*100=\frac{69*5}{2}=35*5=175

Result should be less than 175.

If you have choices as 165, 167, 169, 170, 171, better use long division of 69/41 and multiply by 100 by shifting decimal 2 digits to the right.

retro · Answer

Generally I follow the common factor strategy. In this case, 46 seems to be a strategy.
Coming to decimals in the denominator, they are best handled by drawing up equivalent fractions. In your case, .82 is almost 4/5. So I would calc 138/.82 as 138*5/4 = 34.5*5 nearly 172.5. So any answer that is as close to this as possible would be my pick.
Regards
Rahul

walker · Answer

If you are looking for a fast estimation technique, here is how I would estimate the expression:

138/.82 ~ 140/.80 -->1400/8 --> 350/2 ~ 175

If you need more precise estimation, you can move backward to correct your answer. In my calculation I overestimate 138 (140 is about 1.5% larger) and underestimate 0.82 (0.8 is about 2.5% lower). so, the more precise estimation would be 175 - (1.5% + 2.5%)*175 ~ 175-7 ~ 168. It seems to be difficult but in fact it's not if you know how to estimate small percentages fast. For example, 1% of 175 is 1.75, so 4% of 175 is 2*2*1.75 = 7.

Silver89 · Answer

TIP  for multiplication and division always use fractions 
and decimals for summation and subtraction  
138/0.82= 138/(82/100)= 138*(100/82)=69*(100/41)=69*2.5=69*2 + 69*0.5 = 172.5 ( i rounded 100/41 to 100/40 )
you can round 69 to 70 then it become easier 70*2.5=175

mourinhogmat1 · Answer

Most important concept was to remember that when you round up numerator and denominator you should remember by how much you are rounding up.

vinayrsm · Answer

Thanks for these tips!

EMPOWERgmatRichC · Answer

Hi All,

While this is an old series of posts, there are tips to be had beyond the obvious 'mathematical advice' offered herein. While it might be tempting to get 'caught up' in the calculations (since the Quant section of the GMAT does require the use of THAT skill), the Quant section of the GMAT is NOT a 'math test', so you should be on the lookout to NOT do any unnecessary math.

In certain DS questions, simply 'setting up' the work is enough to determine sufficiency or insufficiency, so a big calculation is not required. In certain PS questions, the answer choices are 'spaced out' enough that rounding or estimation is the faster method to get to the correct answer (and sometimes the prompt itself will TELL YOU to estimate). In many cases, if you find yourself thinking "it will take forever to do all of this math", then there is probably another way to approach the question.

GMAT assassins aren't born, they're made,
Rich

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

Can Someone Please Help Me( Division Strategy)

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards