Series and Sequences

Fast trick to solve Series & sequences

Find the wrong numbers in the series?

1) 307 , 306 , 297 , 272 , 223 , 145 , 21

Lets check the difference between numbers-

306 - 307 =-1

297 - 306 =-9

272 - 297 =-25

223 - 272 =-49

145 - 223 =-78

21 - 145 =-124

The difference of the two consecutive numbers are- -1 , -9 , -25 , -49 , -78 , -124 ,

So it is clear that

12 = 1

32 = 9

52 = 25

72 = 49

so next number should be 92 = 81

Now 223 - 81 = 142

307 , 306 , 297 , 272 , 223 , 145 , 21

So the wrong number is 145


2) 7 , 14 , 28 , 66 , 112 , 224 , 448

as we see -

7 * 2 = 14

14 * 2 = 28

28 * 2 = 56

56 * 2 = 112

112 * 2 = 224

224 * 2 = 448

7 , 14 , 28 , 66 , 112 , 224 , 448

So the wrong number is = 66