How to find interest using numbers other than 100 and having your answer be a percentage.

27/220.  

Step-by-step explanation:

To get £2.50 Pita has to take two pound coins and one 50p coin.

The probability of picking £1 then £1 then 50 p =  3/12 * 2/11* 9/10

= 9/220.

The number of possible arrangements of  2 pounds and 1 50p

= £-£-50, £-50-£ and  50-£-£.

= 3

So the required probability = 3 * 9/220

= 27/220.