300-070 · Question #373
Which number is the result of applying phone number mask 1234X5XX to number 54321?
The correct answer is E. 12344521. Cisco CUCM external phone number masks replace each X positionally by right-aligning the original directory number digits - each X at position n from the right in the mask is replaced by the digit at position n from the right in the source number.
Question
Which number is the result of applying phone number mask 1234X5XX to number 54321?
Options
- A12344321
- B12355321
- C12354521
- D12354321
- E12344521
How the community answered
(35 responses)- A9% (3)
- B3% (1)
- C3% (1)
- D14% (5)
- E71% (25)
Why each option
Cisco CUCM external phone number masks replace each X positionally by right-aligning the original directory number digits - each X at position n from the right in the mask is replaced by the digit at position n from the right in the source number.
12344321 results from an incorrect substitution that does not follow the right-aligned positional mapping rule for the X at position 4 from the right.
12355321 incorrectly places a repeated '5' into an X position, which does not correspond to any digit from the source number at the correct positional offset.
12354521 swaps the values for the X positions, reversing the order of digits '4' and '5' due to misapplying the substitution direction.
12354321 results from a left-to-right sequential digit substitution that ignores the right-aligned positional nature of the mask algorithm.
Mask 1234X5XX has X characters at right-positions 1, 2, and 4. Applying right-aligned positional substitution to number 54321: right-position 1 yields digit '1', right-position 2 yields digit '2', and right-position 4 yields digit '4'. Inserting these into the mask gives 1, 2, 3, 4, [4], 5, [2], [1] = 12344521.
Concept tested: CUCM external phone number mask X substitution rule
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