Lesson 3 of 13
Numbers that read the same both ways
Show on a big screenRead 121 forwards, then backwards. Both ways give 121. Read 305 backwards. It becomes 503.
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Step 1 of 4
- 121 forwards.
- 121 backwards — same. A palindrome!
- 305 forwards.
- 503 backwards — different. Not a palindrome.
The rule
A number that reads the same both ways is a palindrome. To check, reverse the digits: write them backwards.
Not a palindrome yet? Reverse and add. Add the number to its reverse. Repeat until you get a palindrome.
Example
The reverse of 47 is 74. 47 + 74 = 121. One step gives a palindrome.
The reverse of 68 is 86. 68 + 86 = 154. The reverse of 154 is 451. 154 + 451 = 605. The reverse of 605 is 506. 605 + 506 = 1111. Three steps.
Watch out!
A number like 10, 40 or 250 ends in 0. It is not a palindrome. A number cannot start with 0. So its reverse does not match.
Try the lab to finish this lesson.