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f(n) = 1n*2n*3n*4n*...*nn = n^n*n!
f(100) = 100^100*100!
We have formula to calculate trailing zeros from 100! = 100/5+100/5^2 = 24
100^100 has 2*100 = 200 ending zeros
Total = 24+200 = 224

Answer: D
Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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I am timing all my answers and giving myself only 3 mins to write them.
N*1, N*2 .....N*m
f(100) = 100*1, 100*2 .... 100*100
Take 100 common 100( 1*2.....100)
100*100!
Number of zeroes in 100! are (100/5 + 100/25 = 24 zeroes)
Total zeroes are 26
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Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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f(n) is the product of n consecutive positive multiples of n.

f(2) = 2*4

f(3) = 3*6*9
.
.
.
.
.

f(100) = 100*200*300*400*500*...............*10000

= 100^100* (1*2*3*4*5*6*....100)

= 10^(2*100) * 100!

= 10 ^200 * 100!

10^200 contains 200 zeroes.

100! Contains (20+4) = 24 zeroes.

The number of Zeroes = 200+24 = 224 Zeroes.

Option D
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Here, f(100)=100*1 + 100*2 +.....+ 100*100 = 100(1+2+.....+100) =100(100!)

Now to find the number of zeroes in 100!, we have to find the power of 2 and 5 in 100!, or more cleverly, just the power of 5 since that is the limiting factor.

100/5+100/25 =24

100 itself has 2 more zeroes. 100*100! Would have 24+2=26 zeroes.

Therefore, Option B
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f(n) = 100^100*100!
+ 100^100 = 2^200 * 5^200 => 200 is the factor of 5
+ 100! - factor of 5: total trailing zeros = 100/5 + 100/(5^2) = 24
Total factor of 5: 200+24+ 224
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f(n)= n x 2 x 3 x......
f(n)= n^ x n!
so for n=100:
f(100)=100^100 x 100!, Trailing zero= Factors of 10 which is 2 x 5
100^100= 2^2 x 5^2 x 2= 200 factors of 5
factors of 5 i 100 = (100/5)+(100/25) = 20+4=24
Total trailing 0= 200+24
Answer is 224
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Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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Multiples of 100 example are 100, 200, 300 .....

So question is how many zeros will be there if we multiple 100 consecutive multiples of 100 then ...

f(100 ) = 100 * 200 * 300 .....

so from 100 to 900 there will be 18 zeros

However 1000 - 1900 again have approximately 21 zeros

so till now we have total 19 consecutive multiples and we can see it will repeat pattern till 9900 ( which is 99th multiple of 100)

So 18 + 21 * 9 =207

So we know it's more than this number so we can approximately say that it is D because it can't be massive number like E

So Ans - D
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f(100) will be 100*200*300*....*10000

f(100) = 100*1 * 2*100 * 3*100 * 4*100 ..... * 100*100

f(100) = 100^100 * 100!

So 100^100 will have 200 trailing 0's and 100! will have [100/5] +[100/25] + [100/125] + ... where [x] denotes greatest integer function.

So , f(100) will have 200+24 = 224 trailing zero's

Answer is D.
Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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One thing to note, options are very far apart, so we don't need a very accurate value.

So we need to find the number of zeroes in the product of 100 consecutive multiples of 100, which is
100*200*300*400*..........*10000.

For every ten multiples, we get 20 zeroes (2 zeroes for every multiple). Then for 100 multiples we get around 200 zeroes. Option D.

The reason why we are estimating here is, apart from direct 0 zeroes in 100, 200, and so on, we get zeroes from a 2*5 pair as well. For example, 200*500, apart from 4 zeroes, we get one extra zero from 2*5. And we can see there will be more such cases, but definitely not as huge as 2200 more zeroes.

Or we could get the power of 5 (since the number of 5 multiples is less than the number of 2 multiples, it will limit the 2*5 pairs). 500, 1000, 1500, 2000, .....10000, we get 24 5's.
So a total of 224 zeroes.
Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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f(100) = 100 * 200 * ........ 100(100)
= 100^100 (100!)
= 100^100 has 200 zeros

for 100!

find number of 5, 25s multiple

100/5 = 20
100/25 = 4

= 24

ans is 200 + 24 = 224
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Bunuel
The function f(n) is defined for all positive integers n, where n > 1, as the product of n consecutive positive multiples of n. How many zeros does f(100) end with?

A. 24
B. 26
C. 143
D. 224
E. 2400

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100 * 1 * 100 * 2 * 100 * 3 .... 100 * 100

(100)^100 * 100!

(10)^200 * 100!

Power of 5 in 100! = 20 + 4 = 24

10*200 ends with 200 zeros

and 100! ends with 24 zeros

Total = 200 + 24 = 224

Option D
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f(100) = 100*200*300.....100*100 => (100)^100 (1*2*3*4*5...100) => 10^200*(100!)
Power of 10 in 100! = power of 5 in 100! = 100/5+100/25 = 20+4 = 24

Total power of 10 = number of zeroes = 200+24 = 224
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f(100) = 100*200*...100^100
= 100^100*(1*2*3....*100)

Each 100 have 2 zeroes, so hundred 100s would have 200 zeroes.

Then each pair of 2 and 5 can lead to one zero and since multiples of 5 would be less than 2, the total zeroes forming should be the count of multiples of 5.

In the remaining set there are (20+4) = 24 fives are possible.

Adding, the answer should be (D) 224
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f(100) = 1*100 * 2*100 * 3*100 *...* 98*100 * 99*100 * 100*100 = 100! * 100^100

Number of zeros of 100! (count number of 5's) = [100/5] + [100/25] = 20+4=24
Number of zeros of 100^100 (count number of 5's) -> (2^2 * 5^2)^100 = 2^200 * 5^200 -> 200 zeros

200+24=224

IMO D
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f(100) = 1*2*3*4*...*100 * 100^100

As 10=2*5, the number of 0's is given by the number of 5's because the number of 2's is much greater than the number of 0's.

The number of 5's in 100! is calculated using 100/5 + 100/(5^2) = 20+4=24
The number of 0's in 100^100 is 100*2=200

Total: 200+24=224

Answer D
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We know that,
f(n) -> Product of n consecutive multiples of n
=> f(n) = n*2n*3n*4n*....nn = n^n * (1*2*3*4*5*...) = ^n * n!

We need to know number of zeros in f(100)
So,
f(100) = 100^100 * 100!

Its possible to count 0s by finding how many factors of 5 are present (Since more 5s than 2s when counting factors of 10)
Factors of 5 in 100^100
=> 100^100 = ((2^2)*(5^2))^100

Factos of 5 = 2*100 = 200

Factors of 5 in 100!
=> [100/5] + [100/25] = 20 + 4 = 24

Total factors of 5 in f(100) = 200+ 24 = 224

D. 224
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multiples of 100: 100, 2*100, 3*100... 100*100
grouping numbers in their product: (1*2*3*...100)*(100^100) = 100! *(100^100)

In 100^100 there are 100*2=200 zeros
In 100! there are 100/5 + 100/25 = 20+4=24 zeros

200+24=224

The answer is D
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