Unit 2 · Number Theory
Digit Sum 11 · Reversed +27 — What Is the Number?
Lesson 9 of 15
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About this lesson
Now let's step into one of the most elegant corners of Number Theory: puzzles where the number itself is unknown and the clues are hidden in its individual digits. These questions reward students who can translate plain English into a pair of equations.
Chapters
0:00Introduction
0:24The Question
0:50Clue 1 — Sum of the digits
1:20Clue 2 — Reversing the digits
1:41Testing the options
2:14Answer & strategic exam tip
2:59Correct answer
Question
The sum of the digits of a two-digit number is 11.
When the digits are reversed, the number increases by 27.
What is the original number?
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