Question

Replace the ? with an appropriate number from the given alternatives.

$25,49,89,145,217,(?)$

• A. 305
• B. 327
• C. 309
• D. 303

Answer 1

Answer: (A)

305

Given series is : $25,49,89,145,217,(?)$
Rationale: Difference between the consecutive numbers is $24,40,56$ and $72$.These numbers are multiples of $4$ and can be written as
$24=4\ast 6$
$40=4\ast 10$
$56=4\ast 14$
$72=4\ast 18$
We can observe that the multipliers increment by 4
Hence the next number(differentiating number) will be $4\ast 22=88$
So,the difference between 217 and the missing number of the series is 88 ==> the missing number is $217+88=305$
Hence, option 'C' is correct.