Question

3. 4,9,20,43, ?
(a) 80
(b) 90
(c) 75
(d) 85​

Answer 1

The difference between

4 to 9 is 5

and 9 to 20 is 11

and 20 to 43 is 23

Now, find relation between the difference.

5 to 11

=> ( 5×2 ) + 1 = 11

11 to 23

=> ( 11×2 ) + 1 = 23

then, the next difference is

=> ( 23×2 ) + 1 = 46 + 1 = 47

Hence, the next number is

43 + 47 = 90 (b)

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Answer 2

The difference between

4 to 9 is 5

9 to 20 is 11

20 to 43 is 23

Now, find relation between the difference. 5 to 11

=> ( 5×2) + 1= 1

11 to 23 =>

=> ( 11×2) + 1= 23

then, the next difference is

=> ( 23x2) + 1 = 46 + 1= 4

Hence, the next number is 43 + 47 = 90 (b)

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