So this world shatteringly large telescope spies a planet around a star many light years away and is so powerful it can see right down to the surface and tell how many grains of sand there are on the surface of a beach. They are not looking at a beach however, but a classroom with smaller aliens watching a teacher write some numbers on a greenboard:

13 + 15 = 31

10 X 10 = 100

6 X 3 = 24

How many fingers do they have on their hands? Each one of course, not all of them!

From what I can gather they either inbreed a lot and hence differing number of digits on each hand, or they have one hand or they have one finger on a number of hands or maybe tentacles.

Originally posted by deriver69 From what I can gather they either inbreed a lot and hence differing number of digits on each hand, or they have one hand or they have one finger on a number of hands or maybe tentacles.

The telescope did reveal that but that was a large group on another continent. This bunch is more stable genetically and all have the same number of fingers.

10X10 = 100 This is trivial for all number systems

13 +15 =31 so 3 +5 = 11 which means that two odd numbers give an odd number. That means that the number system is odd, so there can't be the same number of digits on an even number of hands, so we have to deal with a race of three hands. This conditions would also claim that it is the number 7. Since the number 8 is represented by 11.

Is this combatible with
6*3=24? It is 18 is 24 in the 7-system.

Now either the aliens have one hand with seven fingers of seven hands with one finger...

Originally posted by Ponderable from the three informations given:

10X10 = 100 This is trivial for all number systems

13 +15 =31 so 3 +5 = 11 which means that two odd numbers give an odd number. That means that the number system is odd, so there can't be the same number of digits on an even number of hands, so we have to deal with a race of three hands. This conditions would al ...[text shortened]... em.

Now either the aliens have one hand with seven fingers of seven hands with one finger...

Or two hands, 3 fingers on one and 4 on the other. Good job. Base 7 it is.