Question

How many such digits are there in the given series each of which, when subtracted from the following digit, gives 1 as the result?

6 7 8 9 8 9 8 7 9 7 7 8 9 7 8 7 6 9 6 8 9 7 7 9 8 9 7 7 6 6 8 7

• A. Three
• B. Four
• C. None
• D. More than four

Hint:

When a question refers to “the following digit,” check consecutive ordered pairs $(d_i,d_i+1)$ and apply the stated difference or sum condition directly.

Answer 1

The Correct Option is D

Step 1: Translate the condition.
“For a digit $d_i$ and its follower $d_{i+1}$, $(d_{i+1}-d_i)=1$.”
So we count all consecutive pairs $(d_i,d_{i+1})$ where $d_{i+1}=d_i+1$.
Step 2: Scan the series.
The qualifying pairs are:
$(6,7)$, $(7,8)$, $(8,9)$, $(8,9)$, $(7,8)$, $(8,9)$, $(7,8)$, $(8,9)$, $(8,9)$
⇒ total $=9$ pairs. \[ \boxed{9\ \text{pairs} ⇒ \text{More than four}} \]