MathDB

One thousand students participate in the

2011

Canadian Closed Mathematics Challenge. Each student is assigned a unique three-digit identification number

abc,

where each of

a, b

and

c

is a digit between

0

and

9,

inclusive. Later, when the contests are marked, a number of markers will be hired. Each of the markers will be given a unique two-digit identification number

xy,

with each of

x

and

y

a digit between

0

and

9,

inclusive. Marker

xy

will be able to mark any contest with an identification number of the form

xyA

xAy

Axy,

for any digit

A.

What is the minimum possible number of markers to be hired to ensure that all contests will be marked?

7

Problems(1)