The sum of any set of postiive integers from 1 to n including n is equal to n(n+1)/2
In this instance, 69 x (69 + 1) / 2 = 2415, therefore, the sum of the numbers 1 to 69 is 2415.
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69 + 18 = 67
There are 69 odd numbers between 20 and 158.
First, take 137 ÷ 2 and you get 68.5. 68.5 is the average. What two numbers average 68.5, 68 and 69. The same two numbers equal 137.
69 = 3 * 23
They all read the same way upside down.