If P = (n)(n - 1)(n - 2) . . . (1) and n > 2, what is the largest value of integer n where P has zero as its last 6 digits and a non-zero digit for its millions place?
(A) 29
(B) 30
(C) 34
(D) 35
(E) 39
Shouldn't the answer be A.
The OA says C.
If you count the number of 5s in the number that should give you the number of leading zeros.
29 has six 5s. So thereby six leading zeros.
Can you please let me know if the above is correct. How is OA C?
leading zeros
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- sanju09
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gmatrant wrote:If P = (n)(n - 1)(n - 2) . . . (1) and n > 2, what is the largest value of integer n where P has zero as its last 6 digits and a non-zero digit for its millions place?
(A) 29
(B) 30
(C) 34
(D) 35
(E) 39
Shouldn't the answer be A.
The OA says C.
If you count the number of 5s in the number that should give you the number of leading zeros.
29 has six 5s. So thereby six leading zeros.
Can you please let me know if the above is correct. How is OA C?
If P has zero as its last 6 digits and a non-zero digit for its millions place, then 29 is not the smallest n that ensures it. It's 30 in fact.
2 zeros when 1 to 10 is multiplied out
2 more zeros when 11 to 20 is multiplied out
2 more zeros when 21 to 30 is multiplied out
Hence, 30 is the minimum n, a seventh zero would appear when n takes 35, till then there would remain six zeros as its last 6 digits when the largest n is [spoiler]34.
C[/spoiler]
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The approach I tried was to count for number of 5s in the number.
Since a combination of 5 & 2 will give a 10, so thereby we can find leading zeros.
Take 30!
30! has seven 5s and more than seven 2s.
So we have seven 10s -> seven leading zeros.
Can you tell me what is wrong with this approach.
Since a combination of 5 & 2 will give a 10, so thereby we can find leading zeros.
Take 30!
30! has seven 5s and more than seven 2s.
So we have seven 10s -> seven leading zeros.
Can you tell me what is wrong with this approach.
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the answer is c.
30..25...22...20...15...12...10...5...2 when these are multiplied you get 6 zeros . so as per the options the 34 will give you the answer with a non zero in the million place...
pls correct me if i am wrong..
30..25...22...20...15...12...10...5...2 when these are multiplied you get 6 zeros . so as per the options the 34 will give you the answer with a non zero in the million place...
pls correct me if i am wrong..
- sanju09
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I rechecked, and found you as correct. [spoiler]A[/spoiler] should be the right answer here.gmatrant wrote:The approach I tried was to count for number of 5s in the number.
Since a combination of 5 & 2 will give a 10, so thereby we can find leading zeros.
Take 30!
30! has seven 5s and more than seven 2s.
So we have seven 10s -> seven leading zeros.
Can you tell me what is wrong with this approach.
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
- sanju09
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gmatrant's approach and claim, both are correct; 25 contains 2 fivesspacealtgrctrl wrote:the answer is c.
30..25...22...20...15...12...10...5...2 when these are multiplied you get 6 zeros . so as per the options the 34 will give you the answer with a non zero in the million place...
pls correct me if i am wrong..
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
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IMO - ans shd be A
1*10 -> 10 (1 zero)
2*5 -> 10 (1 zero)
15*6 -> 90 (1 zero)
20 --> (1 zero)
25 * 4 -> 100 (2 zero)
total of 6 zeros , if we increase our count to 30 - that will result in at least 7 zeros ...
So it shd be A.
What is the source of problem.
And if its official problem - how can we ask Expert to post their suggestions.
1*10 -> 10 (1 zero)
2*5 -> 10 (1 zero)
15*6 -> 90 (1 zero)
20 --> (1 zero)
25 * 4 -> 100 (2 zero)
total of 6 zeros , if we increase our count to 30 - that will result in at least 7 zeros ...
So it shd be A.
What is the source of problem.
And if its official problem - how can we ask Expert to post their suggestions.
Thanks
Puneet
Puneet
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As others have noted, 25 has two 5s, not just one.lokesh r wrote:the answer must be C.
We must count number of 5's.
3x4x5x..10x..x15..x20..x25..29
So, when we calculate 25! (the definition for p is simply p=n!), we get 6 5s (5, 10, 15, 20, 25, 25) giving us a number that ends in 6 0s (since we have lots and lots of 2s).
We want the biggest number that gives us exactly 6 0s; since 30 will give us a 7th, the largest possible value for n is 29.
As always, please provide the source for all of your questions - where is this one from?
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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