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Wrong Number: Sometimes, we are asked to find out a wrong number in the series. Questions based upon wrong number seem a bit tedious. In order, to solve wrong number questions quickly within seconds we should have expertise in handling series questions. If you are not able to identify the wrong number by considering the series from the beginning then you should start backwards. Example 3: Find the wrong number in the following series 11, 42, 59, 67, 71, 73, 74 Solution: In this question if you start from the beginning, then the first difference is 31, then the difference is 17, then the difference is 8. So, we are not getting an appropriate pattern. So, lets start backwards, first difference is 1, second difference is 2, third difference is 4. So we can say then the next differences should be 8, 16, 32. So, now we have a clue. 11 + 32 = 43, 43 + 16 = 59 So, the wrong number in the series is 42. Example 4: Find the next number in the following series 6, 15, 33, 69, 141, ? Solution: On observing the series we can say that next number in the series is almost double of the previous number in the series. So, multiplication factor used in the series is 2. Logic used is 6*2 + 3 = 15; 15*2 + 3 = 33; 33*2 + 3 = 69; 69*2 + 3 = 141; 141*2 + 3 = 285 Example above is an example of a question involving a constant multiplication factor and a different addition factor. Questions based upon the concept of different multiplication factor are a little trickier as compared to questions involving a constant multiplication factor. Let us consider an example that involves a different multiplication factor. Replacing the wrong number: Sometimes we may be asked a question in which we have to find a number that should replace the wrong number. In order to solve such questions we need to first identify the pattern that is used in the series and then try to identify the number that should replace the wrong number. Twin Series: Sometimes we may be asked a question in which we are given two series. From the first series we have to identify the sequence/pattern that has to be applied on the second series. |