In this number analogy, “99 is to 101 as 100 is to ______”. Choose the number that completes the pair so that both sides follow the same simple numerical pattern.

Introduction / Context:
This is a straightforward number analogy that tests recognition of a simple addition pattern. We are given 99 : 101 and asked to extend the same relationship to the pair 100 : ?. Identifying the rule between 99 and 101 will allow us to determine which of the given options correctly completes the analogy.

Given Data / Assumptions:

• First pair: 99 maps to 101. • Second pair: 100 must map to an unknown number. • Options: 90, 110, 111, 102. • We assume a simple arithmetic operation such as addition or subtraction that is applied consistently.

Concept / Approach:
Looking at 99 and 101, the most direct relationship is that 101 is 2 more than 99. That is, 101 = 99 + 2. When a simple constant addition works cleanly for the first pair, it is usually the intended pattern in basic analogy questions. We then apply the same +2 operation to 100 and match the result with one of the answer choices.

Step-by-Step Solution:
Step 1: Compute the difference between 99 and 101. 101 − 99 = 2, so the second number is the first number plus 2. Step 2: Apply this pattern to the second pair. If 100 follows the same rule, the related number should be 100 + 2 = 102. Step 3: Check the options. Only option 102 matches this value, so it is the correct answer.

Verification / Alternative check:
To confirm, we can rewrite the analogy in formula form: a : (a + 2). For the first pair, a = 99 gives 99 : 101. For the second pair, a = 100 gives 100 : 102. This is consistent and uses exactly the same operation. No other option can be justified by a single simple arithmetic rule that also explains the first pair as cleanly as +2 does.

Why Other Options Are Wrong:
• 90: This is 9 less than 99, not 2 more, and there is no symmetric relationship with 99 that mirrors 99 : 101. • 110: This is +10 from 100, but 101 is not +10 from 99, so the pattern would not be consistent. • 111: This is +11 from 100; again this does not match the +2 pattern established by 99 : 101.

Common Pitfalls:
Some candidates attempt to interpret 99 : 101 as “two prime neighbours around 100” and then overcomplicate the second pair. But the question provides a simpler interpretation: a constant difference of 2. Analogy questions usually favour the cleanest, most direct pattern that works for all given pairs, which in this case is simple addition of 2.

Final Answer:
The correct number that completes the analogy is 102.