how many such numbers are there between 1 and 500 which are multiples of 3 and 7 or of both 3 and 7???
211
212
213
214
help asap!! plzz!!
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- AIM TO CRACK GMAT
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Multiples of 3:AIM TO CRACK GMAT wrote:how many such numbers are there between 1 and 500 which are multiples of 3 and 7 or of both 3 and 7???
211
212
213
214
3,6,9,....,498
Total = (498 - 3)/3 + 1 = 495/3 + 1 = 165+1 = 166
Multiples of 7:
7,14,21,...,497
Total = (497 - 7)/7 + 1 = 490/7 + 1 = 70 + 1 = 71
Multiples of (3*7) = 21:
21,42,...,483
Total = (483 - 21)/21 + 1 = 462/21 + 1 = 22 + 1 = 23
Grand total = 166 + 71 - 23 = 214
Choose D
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SUBTRACT THE OVERLAP.AIM TO CRACK GMAT wrote:How many integers between 1 and 500 are multiples of 3 or 7 or of both 3 and 7?
211
212
213
214
Total = Multiples of 3 + Multiples of 7 - Multiples of 21.
When we count the multiples of 3 and the multiples of 7, the OVERLAP between the two groups -- the multiples of 21 -- are counted TWICE.
So that the multiples of 21 are not double-counted, we must subtract them from the total.
The endpoints of the range are 1 and 500, implying a total of 500 integers.
Since neither endpoint is divisible by 3 or 7, we can can quickly count the multiples of 3, 7 and 21 by determining how many times 3, 7 and 21 each divide into 500.
Multiples of 3 between 1 and 500:
500/3 = 166.
Multiples of 7 between 1 and 500:
500/7 = 71.
Multiples of 21 between 1 and 500:
500/21 = 23.
Thus:
Total = 166 + 71 - 23 = 214.
The correct answer is D.
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Hi AIM,
Mitch has provided the most direct way to answer this question, so I won't rehash that. I will point out that this question is NOT in proper GMAT format. You should be skeptical of any resources that don't properly match the style of the real test.
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Mitch has provided the most direct way to answer this question, so I won't rehash that. I will point out that this question is NOT in proper GMAT format. You should be skeptical of any resources that don't properly match the style of the real test.
GMAT assassins aren't born, they're made,
Rich
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I think this question would be better worded as:
how many such numbers are there between 1 and 500 which are multiples of 3 OR 7, or of both 3 and 7???
The distinction between AND and OR makes a real difference in meaning.
Otherwise, the answer is 23.
how many such numbers are there between 1 and 500 which are multiples of 3 OR 7, or of both 3 and 7???
The distinction between AND and OR makes a real difference in meaning.
Otherwise, the answer is 23.