If the number of observations is odd, the number in the middle of the list is the median. This can be found by taking the value of the (n+1)/2 -th term, where n is the number of observations. Else, if the number of observations is even, then the median is the simple average of the middle two numbers.

To find the sum of first n odd numbers we can use the formula S_n= n². For example, to calculate the sum of odd numbers between 1 to 10, we know that n = 5. Thus, S₅ = 5² = 25.

The 'Lucky 15' bet is a popular multiple bet, which involves 4 selections, amounting to 15 invdividual bets across those. This bet type consists of 4 singles, 6 doubles, 4 trebles and 1 four-fold accumulator. In order to gain a return, the bettor requires just one of the four selections to be settled as a winner.

You pick your 10 winners and then make every possible fivefold bet from them all. This is called a fivefolds from 10 selections bet  but if you were unsure of a couple of games you might just pick the winner of eight of the 10 matches and opt for a fivefolds from eight selections instead.