Answer: 40 and 41
40+41 = 81
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Step-by-step explanation
Using quick mental math, half of 81 is around 40 since 81 is close to 80.
Then we check a few pairs of values
- 39+40 = 79
- 40+41 = 81 ... we found the answer
- 41+42 = 83
Note that the results are odd. This is because adding an integer n to the next one n+1 gets us 2n+1 which is always odd.
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Here's a more formal approach
n = some number
n+1 = number just after n
n+(n+1) = 81
2n+1 = 81
2n = 81-1
2n = 80
n = 80/2
n = 40
Therefore the two numbers are n = 40 and n+1 = 40+1 = 41