Dr. Math's four-digit house number ABCD contains no zeroes and can be split into two different two-digit primes ``AB'' and ``CD'' where the digits A, B, C and D are not necessarily distinct. If each of the two-digit primes is less than 40, how many such house numbers are possible?

 Jul 20, 2018

The two digit primes < 40 are

11, 13, 17, 19, 23, 29, 31, 37


Any two of these eight can be selected  =  C(8,2)  = 28


And each of these can be arranged in two ways


So...the total number possible house  numbers  is  2 * 28  =  56



cool cool cool

 Jul 20, 2018

Yes it is correct thank you very very much

 Jul 21, 2018

7 Online Users


New Privacy Policy

We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive information about your use of our website.
For more information: our cookie policy and privacy policy.