The Best Approach to tackle Problems involving 7 as divisor

[farukh_a]

In the MGMAT Number Properties Strategy Guide, no rule is listed for divisibility by 7.

There is another comment at the end of page 14:

"The simplest way to check for divisibility by 7, or by any other number not found in this list is to perform long division"

Does this mean that MGMAT suggests that all those rules that we see on different blogs etc are actually way too cumbersome and time consuming to be practically useful on GMAT?

PS: I can understand that mostly all these rules that we see on the internet are very complex but I just wanted MGMAT's take on this so that I don't waste time remember those intricate formulas that in the end would cost me more time.

Regards
Farukh

[gpinder77]

In the MGMAT Number Properties Strategy Guide, no rule is listed for divisibility by 7.

There is another comment at the end of page 14:

"The simplest way to check for divisibility by 7, or by any other number not found in this list is to perform long division"

Does this mean that MGMAT suggests that all those rules that we see on different blogs etc are actually way too cumbersome and time consuming to be practically useful on GMAT?

PS: I can understand that mostly all these rules that we see on the internet are very complex but I just wanted MGMAT's take on this so that I don't waste time remember those intricate formulas that in the end would cost me more time.

Regards
Farukh

for 7, simply double the last digit and subtract it from the digits in front of it.

so for example....is 140 divisible by 7? 0x2=0. 14-0=14. and 14 is divisible by 7, therefore so is 140

[tim]

nice trick, but yes in general it's best not to waste a bunch of time memorizing obscure tricks when they won't save you much time anyway..