Simple Multiplication

[Adam]

This may sound like a stupid question given the fact that I'm so far into studying..........but I run into a lot of trouble when I get problems that involve multiplying........I don't mean 3x4 and stuff like that....but anything that involves double digits +.

For example: 1.7x2.27, 3.471x9.0097..........those are obviously just random numbers, but how do I go about solving them?!?!?!?! I've looked online and found some examples but they don't seem to help me.....Does anyone have a good way of doing this? Even if it's something from 4th grade math (which it probably is) I would greatly appreciate it.

Thanks in advance!

[sumithshah]

Look up something called Vedic Mathematics - it reduces multiplication to two steps of addition and subtraction

[Sudipto2002]

This is from Vedic Maths:

Some simple examples: Multiplying numbers close to 10, 100, 1000 etc.

Say 99x98
99 can be written as -01 (think 100-99 = 01, 01 since there are 2 0's in 100, for 998 you will have 002)
98 can be written as -02
Cross subtract (99-02 or 98-01) and you get 97 as the left 2 digits and multiply 01 and 02 to get right hand digits. Your answer is 9702

Another example:
992 - 008
x 996 - 004
----------------
888 032

The one I use frequently use is the 1 step multiplication. If you want to multiply say 56 x 32

You can break it down into 6x2 + (5x2 + 6x3 + 1 which you carried over from last step) + (5x3 + 2 that you carried over from last step)

6x2=12 (put down 2 as the last right hand number and carry over 1)
5x2+6x3+1=29 (put down 9 and carry over 2)
5x3+2 = 17
So your answer is 1792

You can extened this to any number of digits lets say 492x786
6x2 + (9*6+8*2 + carry) +(4*6+7*2+9*8 + carry) + (4*8+7*9+carry) + (7*8+carry)

Hope this helps. Google Vedic Mathematics for more such applications. You can also buy the Vedic Mathematics book at Amazon.

[StaceyKoprince]

The first place you should look is not in any book but at the answer choices. When they give you stuff like that, you don't actually have to do the real math. You can usually estimate. You can confirm that hunch by looking at the answers - are they far enough apart to make estimation feasible? Is there some way for you to tell whether you're going to get, say, a 2 in the units' digit and only one answer has a 2 in the units' digit? Etc.

These questions are all designed to be done (by someone anyway) in 2 minutes. And they don't expect us to be human calculators. :) So something else is going on. Don't get sucked into ridiculous calculations - look for the shortcut instead.

So 1.7 becomes 1.5 (or 3/2) and 2.27 becomes 2.25 or 9/4. And, honestly, most of the time you don't even have to be that close - you can usually round to whole numbers or, at most, halves.

[cooper2248817]

Why don't you round these numbers and get an approximate answer. GMAT doesn't expect you to calculate these numbers. You may be a type of person that wants the exact number. Round and move on and trust your judgment. Don't waste your time checking and re-checking. Trust yourself!!!!!!!!!!!!!!!!!!!!!!1


1.7x2.27----------2*2= should about little less the 4 so approximate to 3.7


3.471x9.0097-------3.5*9== approximate it to 31.5.

Look at the fraction/percent/ fdp study guide. It should help you.

Hope this helps.

[StaceyKoprince]

exactly :)