Similarly, if n is less than or equal to 26/7, then the value of n can be 4, 5, 6, 7, 8, 9, 10.
Then substitute the values respectively and find that n is 6.
2. 1/4+2/4+……+n/4 = n(n+ 1)/8
( 1+2+……+n)/4 = n(n+ 1)/8
The left side can be based on the formula (the sum of the first and last items multiplied by the number of items divided by 2).
[( 1+n)n/2]/4 = n(n+ 1)/8
3.2/5