#1**+10 **

They must start with either the 5 or the 6.

Consider those that start with a 5.

There are 6 digits left that could go in the "tens" position.

For each of these there are 5 digits left that could go in the "units" position.

Hence there are 6*5 = 30 possible 3-digit numbers beginning with 5.

Similar reasoning shows that there are also 30 possible 3-digit numbers beginning with 6.

So there are 60 possibilities in all.

.

Alan
Jan 30, 2015

#1**+10 **

Best Answer

They must start with either the 5 or the 6.

Consider those that start with a 5.

There are 6 digits left that could go in the "tens" position.

For each of these there are 5 digits left that could go in the "units" position.

Hence there are 6*5 = 30 possible 3-digit numbers beginning with 5.

Similar reasoning shows that there are also 30 possible 3-digit numbers beginning with 6.

So there are 60 possibilities in all.

.

Alan
Jan 30, 2015