Copyright © University of Cambridge. All rights reserved.
Well done for giving clear solutions to this
problem. Many of you were able to explain a general strategy.
Tom and Jeevan from Devonshire Primary School said:
If you are trying to make the largest even number using an odd
number you put the odd number in the tens column and in the units
column you put $8$.
But if you're doing it with an even number then you put $9$ in the
tens column and then put the even number in the units column.
Peter, Henry, Charlie, Lulu and Samuel at
Weald C of E Primary School assumed that you could also get a zero.
They went on to think about how you would make the smallest
1.If you get an odd number, put an eight in the units column.
2.If you get an even number, put a nine in the tens column.
3.If you get a zero, put a nine in the tens column.
1.If you get an odd number, add a zero in the units column.
2.If you get an even number, add a one in the tens column
3.If you get a zero, put a one in the tens column.
Homeroom 7 at Kororoit Creek Primary School,
Australia looked at a strategy for making the largest odd number
The largest two-digit odd number we could make is $97$. We
could not make $99$ because we only have one $9$.
If you pulled out an odd number first this should always go in
the 'ones' column. Unless you pull out a number $9$. The $9$ will
always go first because $97$ is the biggest number we can make.
e.g. $97$, $79$, $59$, $39$, $19$.
If you pull out an even number first it should always go in
the 'tens' columns, otherwise your two-digit number will not be
odd. You should still always choose the number $9$ as your second
card to make the largest number possible. e.g. $89$, $69$, $49$,
Well done too to Robert from West Hoathly and
Sophie from Greenacre who also sent very full responses.