Direction : What will come in the place of question mark in following number…

Concept

In an alternating number series, two independent sub-series are interleaved term by term: the terms in the odd positions form one progression and the terms in the even positions form a separate progression. Each sub-series follows its own constant rule, so the key is to read the series in two strands rather than as a single chain.

Application

Split 9.8, ?, 8.9, 11.6, 8, 12.5 into its two strands by position:

1. Odd positions (1st, 3rd, 5th terms): 9.8, 8.9, 8.0 — each term is 0.9 less than the previous, so this strand decreases by a constant 0.9.

2. Even positions (2nd, 4th, 6th terms): ?, 11.6, 12.5 — here 12.5 − 11.6 = 0.9, so this strand increases by a constant 0.9.

3. The missing term is the first member of the increasing even strand. Working one step back from 11.6 gives 11.6 − 0.9 = 10.7.

Cross-check

Read the completed even strand forward: 10.7, 11.6, 12.5 rises by exactly 0.9 each step, and the odd strand 9.8, 8.9, 8.0 falls by exactly 0.9 each step. Both progressions are consistent, confirming the missing value is 10.7.