What should come in place of the question mark 39 39 in the following number series 7 56 399 448 840...........

Quantitative Aptitude(IBPS RRB PO) Number series

What should come in place of the question mark '?' in the following number series?

7, 56, 399, 448, ?, 840, 1183

This questions was previously asked in

RRB PO Prelims (06 Aug, 2023 Shift 1)

792

791

733

581

None

To solve the series, let's look at the differences between consecutive numbers:

- Between 7 and 56: The difference is 49.

- Between 56 and 399: The difference is 343.

- Between 399 and 448: The difference is 49.

Observing these differences:

- 49 is 7²

- 343 is 7³

It follows that every third difference might be a repeat, so:

- Between 448 and the next number: The difference should again be 343.

Therefore:

- 448 + 343 = 791

Thus, the number in place of '?' should be 791.

- Option 2: 791 is correct.

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