Hey found this interesting question while surfing the other forums. I have noticed there are so many different rules related to number properties that are commonly tested on the GMAT. Can we start a thread where we all put togethere all the rules we have come across so far? I am sure this will help a great deal on the GMAT. Any comments?
f(k)
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In a six digit integer N, f(k) is the value of the k-th digi. For example, f(4) is the value of the hundreds digit of N. Is N divisible by 7?
1. f(1) = F(4), F(2) = f(5), f(3) = f(6)
2. f(1) = f(2) = f(3)..... = F(6)
below is the ans I found there and some other interesting comments.
[spoiler]For cond2, all 6 digits are the same i.e 111111 or 555555. Such nos are divisible by 7
For cond2, 1st and 4th, 2nd and 5th and 3rd and 6th digits are the same
Nos are like 123123 or 456456. Such nos are divisible by 7
Hence D
a method of checking divisibility by 7 using altenernating sum of blocks of 3 digits from right to left in Wikipedia.
Form the alternating sum of blocks of three from right to left.
1,369,851:
851 - 369 + 1 =483 = 7 × 69[/spoiler]
f(k)
--------------------------------------------------------------------------------
In a six digit integer N, f(k) is the value of the k-th digi. For example, f(4) is the value of the hundreds digit of N. Is N divisible by 7?
1. f(1) = F(4), F(2) = f(5), f(3) = f(6)
2. f(1) = f(2) = f(3)..... = F(6)
below is the ans I found there and some other interesting comments.
[spoiler]For cond2, all 6 digits are the same i.e 111111 or 555555. Such nos are divisible by 7
For cond2, 1st and 4th, 2nd and 5th and 3rd and 6th digits are the same
Nos are like 123123 or 456456. Such nos are divisible by 7
Hence D
a method of checking divisibility by 7 using altenernating sum of blocks of 3 digits from right to left in Wikipedia.
Form the alternating sum of blocks of three from right to left.
1,369,851:
851 - 369 + 1 =483 = 7 × 69[/spoiler]
