We start to work with this question by underlining the most important information it provides us:All tickets for a concert are the same price.Amy and Dan pay £63 for some tickets. Amy pays £24.50 for 7 tickets. How many tickets does Dan buy?So Amy (A) and Dan (D) purchased x tickets for £63. --> A + D = 63 for x ticketsBut we know that A payed exactly £24.50 for 7 tickets. --> A = 24.5 for 7 ticketsTherefore you can combine these two to find out how much D payed himself. --> D = 38.5 for x-7 ticketsNow we want to find out how much 1 ticket costs. For that just look at A's purchase. She bought 7 tickets that are the same price for £24.50. So if we divide this 24.50 by 7 we get the price of 1 ticket. --> 1 ticket = 24.5/7 = £3.5 Since we know that D bought tickets worth £38.50 and again of the same price, we can calculate the number of tickets he bought himself by dividing the total price with the price of one ticket. --> 38.50/3.50 = 11And there you have your answer: Dan bought 11 tickets on his own.