Advent Calendar 2015 Introduction

Following the fun that was hopefully had from last year's Advent Calendar I am making another one this year!

If you are unsure of what an Advent Calendar is here is a short explanation; to celebrate Christmas many shops sell Advent Calendars. For every day of December up to Christmas these calendars have a small treat which is normally a piece of chocolate.

But of course, why not have a math problem instead? That is exactly what I have decided to do. The problems will be of varying difficulty and like last year I will try to post the problems on the previous day to account for the time zone difference.

Please have fun and I hope you enjoy solving the problems!

Here is a link to the set.