Sunday 21 September 2014

mathematics - Madam I m Adam..please don’t get mad..you will no longer be prime


Take away $ \overline{MAD} $ from $ \overline{MADMADAM} $ to make her prime. $ \overline{ADAM} $ is prime too if he does not get mad: $ \overline{MADADAM}. $


$ M, A, D $ are 3 distinct digits that are to be determined by you so that the statements in this puzzle are true.



Answer



So, we have two prime numbers (MADMADAM-MAD, ADAM).


Consequently, from a more mathematical standpoint,



$M*10,010,001 + A* 1,001,010 + D*100,100 - (M*100 + A*10 + D)$ is prime, as is $A*1,010 + D*100 + M$.




I ran this through a little program that I wrote, and I discovered that there are three distinct solution sets. They are:





  1. M: 1 A: 5 D: 8 --> $15,815,851 - 158 = 15,815,693‬$, which is prime. $5851$ is also prime.







  2. M: 3 A: 1 D: 6 --> $31,631,613 - 316 = 31,631,297‬$, which is prime. $1613$ is also prime.






  3. M: 3 A: 5 D: 6 --> $35,635,653 - 356 = 35,635,297$, which is prime. $5653$ is also prime.





If you're interested, here's the Java program that I wrote to find the answer. It probably isn't super efficient, but it works.





public class Test {

public static void main(String[] args) {
int big = 0;
for(int i = 1; i<=9; i++) {
for(int j = 1; j<=9; j++) {
for(int k = 0; k<=9; k++) { //k (or d) is the only digit which could be 0.
if(isPrime(i*10010001 + j* 1001010 + k*100100 - (i*100 + j*10 + k))&&

isPrime(j*1010 + k*100 + i)) {
big = i*10010001 + j* 1001010 + k*100100 - (i*100 + j*10 + k);
System.out.println("M: " + i + " A: " + j + " D: " + k);
System.out.println(""+i+j+k+i+j+k+j+i+"-"+ i+j+k+"="+big+
", which is prime. "+j+k+j+i+" is also prime.\n");
}
}
}
}
}

public static boolean isPrime(int i) {
boolean prime = true;
for(int j = 2; j<=i/2; j++) {
if (i%j==0) {
prime = false;
break;
}
}
return prime;
}

}

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