Today we are looking at questions 17 and 18 of the 2011 paper A with questions, answers and helpful tips. The answer to question17 is   22.11     One mark. No working needs to be shown. The answer to question 18 is   4     One mark.          Accept 21 and 22 and 23 and 24 Question 17 is a classic addition. Rarely, if ever, will you see an addition question set out in the form needed for using the standard written method. Almost always it will be presented in a horizontal form. This question is likely to catch a few out as the first number has two digits after the decimal point and the second number only has one digit after the decimal point. Beware of the mistake of setting it out like this: 3.81 +18.3 and then adding the 1 and the 3. It’s always a good idea to check an answer by repeating the addition in a different order or trying an equivalent subtraction e.g. 22.11 – 18.3. Question 18 is also a very popular type of question, using ‘how many ways....’. usually these are quite straightforward if they are approached in a logical, well ordered way. One of the best ways to approach this is to start with the highest possible total and then change one disk at a time: i.e. 8 + 8 + 8 = 24 8 + 8 + 7 = 23 8 + 7 + 7 = 22 7 + 7 + 7 = 21 And then realising that other configurations are essentially repeating the above e.g. 7 + 8 + 8 is the same as 8 + 8 + 7. The question actually asks how many different totals can be made, which is four, but the mark scheme does allow for the four totals to be written down. Go to Questions 17 and 18 Go to answers for questions 17 and 18