Open Middle®
Directions: Using the digits 1 to 9 exactly one time each, place a digit in each box two times: once to make a sum that is greater than 700 and once to make a sum that is less than 700. You may reuse all the digits for each sum.
Hint
What place value will be most important to consider? How can you tell whether the sum will be more or less than 700 without adding all of the digits?
Answer
There are many possible answers, including 129 + 453 for a sum that is less than 700 and 987 + 654 for a sum that is greater than 700.
Source: Robert Kaplinsky
135 + 246 = 381
678 + 954 = 1,632
123 + 456 = 579
486 + 631 = 1117
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111+111=222
222+222=444
444+444=888
888+888=1,776
and that,s it.
789 + 236 = 925
345 + 267 = 612
192+483=675, 152+784=936. In both solutions, each digit is used only once, including in the solution.
124 +356
987+654
100 + 753 = 853
510 + 145 = 655
More than 700:
682 + 134 = 816
952 + 367 = 1319
346 + 512 = 858
Less than 700:
213 + 486 = 699
427 + 163 = 590
245 + 316 = 561