Which ten numbers between 700 and 800 can be formed from a number plus it's reversal?
1. 106 + 601 = 707
2. 413 + 314 = 727
3. 324 + 423 = 747
4. 532 + 235 = 767
5. 146 + 641 = 787
6. 155 + 551 = 706
7. 561 + 165 = 726
8. 571 + 175 = 746
9. 284 + 482 = 766
10. 195 + 591 = 786
Explanation:
-The sum of the place value in 100's column adds to either 6 or 7. This is because 299 + 399 (highest 2/3, 3 digit number) equals 698, which is less than 700. And if the first digit equals 7, than the last digit will be 6 or 7.
- The two middle digits of the numbers being added together have to be the same and can only be used once as highlighted. If the highlighted numbers are greater than 5, the last digit is a six. If they are smaller than five, the last digit is a seven.
- The other two numbers, that must equal to either 6 or 7, has to have one number greater than five added with one number less than five. Eg. 4+2=6 and 6+1=7.