Problem
First name
Year 11
School
Sandbach High School
Country
Age
15
Problem 3: Zainab Adnan, Amy Hewitt, Ellie Gosling
Choose a two-digit number with two different digits (e.g. 47) and form its reversal (i.e. 74).
AB and BA are 10A+B and 10B+A
subtract (A+B)
gives 9A and 9B
as a multiple 9(A+B).
Now, subtract the sum of the digits from each of these numbers, and then add the two results. Show that you always obtain a multiple of 9.