Copyright © University of Cambridge. All rights reserved.

'Alien Counting' printed from http://nrich.maths.org/

Show menu


3aliens2aliens
Well here are five Aliens, all from different planets.
They all count using one "hand" except the last one who uses his six tentacles.
So let me introduce them:

1st - Serious "Dubo" who counts in twos;
2nd - The two headed "Threebee" who counts in threes;
3rd - The laughing "Quort", who counts in fours;
4th - The green-headed "Chindi" who (you guessed it) counts in fives;
Finally - The four-eyed "Senda" counting in sixes.

They've come to Earth to learn about us and what we do!
They visit a school and are interested in how many earth children there are in each room.
Dubo starts counting like this (up to what we would call seven and record as "7"):
Pic1

Then the next two:

Threebee and then Quort
Threebee Quort


Then the last two aliens, Chindi and Senda, do their counting:
base5base6
When we do our counting we have units, tens and hundreds. Those hundreds are ten lots of ten.
Notice that when Chindi counts he can only use 0, 1, 2, 3 and 4 whereas we use 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
The aliens go to a classroom and count the children. We would count 30 - but they would record and say that differently.
Here's how they record:
Dubo 11110; 1 (2 lots of 2 lots of 2 lots of 2), 1 (2 lots of 2 lots of 2), 1 (2 lots of 2), and 1 (lot of 2)
Threebee 1010; 1 (3 lots of 3 lots of 3), and 1 (lot of 3)
Quort 132; 1 (4 lots of 4), 3 ( lots of 4), and 2
Chindi 110; 1 (5 lots of 5), and 1 (lot of 5)
Senda 50; 5 (lots of 6)

It would be a good idea to try to see how their counting goes after (our) "7", what they'd say and how they'd record it.

words2

When we humans try to look at what the aliens had written we might put a mask over most of the digits, all except the second from the right!
simplewindow
So when for example we try to look at one of Quort's numbers (suppose 0 0 1 3 1) a mask is over it and all we see is the 3.
Eg window

words1
Find numbers that the aliens used to count the children in the classroom that look the same
to the humans looking at the masks.
For example, to start you off:
When we look at Quort's 3 it looks the same as Senda's 35, or Chindi's 33 etc.
So find one alien's number that would look the same to humans as another alien's number.

Find all the pairs you can.

Some of you might like to go on to say what those numbers would have been if humans had been counting, for example Senda's 35 which humans would have counted as 23 (three 6's and a 5 makes 23).