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(#M40021877) INFOSYS question Keep an EYE

HOW MANY POWERS OF 20 ARE THERE IN 100! ??

Asked In Infosys Ajay Lunia (11 years ago)

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Rahul Kumar Mehta  (11 years ago)

24 will be the correct answer

20 = 5*4 = 5*2*2

now [100/5] + [100/5^2] = 20 + 4 = 24(power of 5 is 24)

now [100/2] + [100/2^2] + [100/2^3] + [100/2^4] + [100/2^5] + [100/2^6] =

50 + 25 + 12 + 5 + 3 + 1 = 96

Power of 2 is 96*2 = 192 (because we have two 2)

so power of 4 will be 192/2 = 96

but we have only 24 power of 5 so we will take only 24 power of 4 instead of 96

Is this solution Helpfull? Yes (12) | No (9)  

Deepankar manduri  (11 years ago)

firstly we ll find out the prime factor of 20 and the factor of 20 is 2 and 5
because ,

20=2*2*5

now we just need to find out how many power of 5 are divisible by 100!

so 100/5= 20
and 100/5^2=100/25=4
100/5^3=100/125 =0 we are counting just integer values on decimal

adding both value we will get 24
and this is the answer

in such typ of question we just need to divide the num by given number's highest prime factor . :)

Is this solution Helpfull? Yes (5) | No   

saikumar  (11 years ago)

24 will be the correct answer

20 = 5*4 = 5*2*2

there fore [100/5]+[100/25]= 20 + 4 = 24
similarly for 2

[100/2]+[100/4]+[100/8]+[100/16]+[100/32]+[100/64]= 50+25+12.5+6.25+3.125+1.5625= it comes around 98

so now we want it for 4 so 98/2= around 49

so foe powers of 20 we have to take common
like we have 24 (5 powers)and 49(4 powers)
common we take 24 (5*4=20 powers)

so ans is 24

Is this solution Helpfull? Yes (2) | No   

BHARGAV ARYASOMAYAJULA  (11 years ago)

20 appears in 20,40,60,80,100(5 times here) in addition to that 20 can be expressed as (5*4) or (2*10).so we have to count the no. of 5's appearing in 100! excluding the above 5 numbers.5 appears once in 5,15,30,35,45,55,70,85,90,95(10 times here) and twice in 25,50,75(6 times here).so total power of 20 in 100! is 5+10+6=21

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Sudharsan  (11 years ago)

only 2
i.e 20^0,20^1

Is this solution Helpfull? Yes (1) | No (2)  

Laxmi Srinivas  (11 years ago)

5 = 100/20 = 5

Is this solution Helpfull? Yes | No (3)  

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