Bunuel wrote:
shaderon wrote:
Hello there
I tried using the following approach. I did end up taking some time.
The numbers to be considered are 2,3,5 & 7.
For 2-digit numbers:
(4 PRIME numbers in the Ten's place)
(4 PRIME numbers in the Unit's place)
4*4 = 16 --- (1)
For 3-digit numbers:
(9 numbers in the Hundred's place i.e 1 to 9)
(4 PRIME numbers in the Ten's place)
(4 PRIME numbers in the Unit's place)
9*4*4 = 144 --- (2)
For 4-digit numbers (till 1500):
(1 number in the Thousand's place i.e. 1)
(5 numbers in the Hundred's place i.e. 0, 1, 2, 3, 4)
(4 PRIME numbers in the Ten's place i.e 2, 3, 5 & 7)
(4 PRIME numbers in the Unit's place i.e 2, 3, 5 & 7)
1*5*4*4 = 80 --- (3)
For 4-digit numbers (1501 to 1570):
(1 number in the Thousand's place i.e. 1)
(1 number in the Hundred's place i.e. 5)
(3 PRIME numbers in the Ten's place i.e 2, 3, 5)
(4 PRIME numbers in the Unit's place i.e 2, 3, 5 & 7)
1*1*3*4 = 12 --- (4)
Adding (1), (2), (3) & (4) ----> 252
Can an Expert evaluate the approach? I want to be sure that I considered the possibilities correctly.
Thanks in advance for the help.
Yes, your solution is correct.
Hello Bunuel and everyone else.
I have been reading the answers and Im on the same page as everyone else but I got answer as 256 because 252 +4 , the 4 comes from single digit number 2,3,5, or 7 only. Hmmmm.... where Im going worng here.
I would like kindly to ask for explanaion what others think on this issue