Find the Number of PrimeNumbers

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rakeen
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Find the Number of PrimeNumbers

Unread post by rakeen » Thu Dec 16, 2010 2:28 pm

I found this in BdMO Div(don't remember the year). It says, A set has 20 'cromic dhonattok purnaa shonkha'. They all are greater than 50. How many Prime Numbers there will be in that set?

$Note:$ hint first.
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AntiviruShahriar
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Re: Find the Number of PrimeNumbers

Unread post by AntiviruShahriar » Thu Dec 16, 2010 4:18 pm

প্রত্যেক $20$ টি সংখ্যার মধ্যে $10$ টি জোড়। বাকি $10$ টির মধ্যে প্রতি $4$ টি বিজোড়ের $1$ টি $3$ দ্বারা বিভাজ্য। $10$/$4$=$2.5$.তাই আমরা $3$ টির জন্য $3$ টি আর $2$ টির জন্য $2$ টি বিয়োগ দিব।
$20$ টি এর মধ্যে $5$ দ্বারা বিভাজ্য আছে $3$ টি, এর মধ্যে $1$ টি $3$,$5$ উভয় দ্বারা বিভাজ্য। আর এক্তা $7$ দ্বারা বিভাজ্য
অতএব, বাকি থাকে $20$-$10$-$3$ or $2$-$3$+$1$-$1$=$5$ or $4$ টি
I am not sure about this solution....i just guessed it........ :roll:
Last edited by AntiviruShahriar on Thu Dec 16, 2010 4:42 pm, edited 1 time in total.

AntiviruShahriar
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Re: Find the Number of PrimeNumbers

Unread post by AntiviruShahriar » Thu Dec 16, 2010 4:34 pm

rakeen wrote:I found this in BdMO Div(don't remember the year). It says, A set has 20 'cromic dhonattok purnaa shonkha'. They all are greater than 50. How many Prime Numbers there will be in that set?

$Note:$ hint first.
sorry আমি hidden করার নিয়ম জানি না। নিচে না তাকিয়ে কর।

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rakeen
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Re: Find the Number of PrimeNumbers

Unread post by rakeen » Fri Dec 17, 2010 4:16 pm

your technique is quite interesting. ektu matha khatalei hoy. :)

thnx
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Muhiminul Maruf
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Re: Find the Number of PrimeNumbers

Unread post by Muhiminul Maruf » Sat Dec 18, 2010 1:08 pm

ansta ki shahriarer ta thik ase????????

AntiviruShahriar
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Re: Find the Number of PrimeNumbers

Unread post by AntiviruShahriar » Sun Dec 19, 2010 1:09 am

rakeen--welxxxxxx.maruf--jani na just guess korsii..tui r 1ta bair korte parle post kor...dekhi thikase naaki

Dipan
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Re: Find the Number of PrimeNumbers

Unread post by Dipan » Sun Dec 19, 2010 9:25 am

The ans should be 3 if there is no twin prime.

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rakeen
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Re: Find the Number of PrimeNumbers

Unread post by rakeen » Sun Dec 19, 2010 10:52 am

@Anti tomar solution ta thik moto bujhi nai. But it helped me a lot.
@Dipan mine is 6. bcoz the question says "possible highest" number of prime.
Of the 10 odd numbers there are 3/4 such numbers that are divisible by 3. But according to question we have to consider, there are 3 such number which are divisible by 3. Again, of the 10 odd numbers there are 2 such numbers that are divisible by 5.But, of the 2(wchich are divisible by 5) numbers, one or two is divisible by 3. But according to question we have to consider, of them only one number is divisible by 3(which is also divisible by 5). So, of the 10 odd numbers there are 3+1=4 numbers which are divisible either by 3 or 5. So we have 10-4=6 such numbers who are not divisible by 2,3,4,5,6,8,9.(I have not consider 7). That means 6 of them are prime
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Re: Find the Number of PrimeNumbers

Unread post by AntiviruShahriar » Sun Dec 19, 2010 12:45 pm

Dipan wrote:The ans should be 3 if there is no twin prime.
proof???????

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Re: Find the Number of PrimeNumbers

Unread post by AntiviruShahriar » Sun Dec 19, 2010 12:53 pm

rakeen wrote:@Anti tomar solution ta thik moto bujhi nai. But it helped me a lot.
@Dipan mine is 6. bcoz the question says "possible highest" number of prime.
Of the 10 odd numbers there are 3/4 such numbers that are divisible by 3. But according to question we have to consider, there are 3 such number which are divisible by 3. Again, of the 10 odd numbers there are 2 such numbers that are divisible by 5.But, of the 2(wchich are divisible by 5) numbers, one or two is divisible by 3. But according to question we have to consider, of them only one number is divisible by 3(which is also divisible by 5). So, of the 10 odd numbers there are 3+1=4 numbers which are divisible either by 3 or 5. So we have 10-4=6 such numbers who are not divisible by 2,3,4,5,6,8,9.(I have not consider 7). That means 6 of them are prime
majhe majhe ami nijeo bujhi na....6 ta prime ase emon example dao to......tomar qs ta poro tumi highest bolso koi?????tobee aj k amar solution nia boshsilam bt oita te vul o thakte parre jokhon prime number 20 tar moddhey 3 ta hoy..j mon 521 to 540 te 3 ta ase.........

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