Explanation
Address the formula, input parameters & values.
Input parameters & values:
The number series 1, 3, 5, 7, 9, . . . . , 139.
The first term a = 1
The common difference d = 2
Total number of terms n = 70
step 2
apply the input parameter values in the AP formula
Sum = n/2 x (a + Tn)
= 70/2 x (1 + 139)
= (70 x 140)/ 2
= 9800/2
1 + 3 + 5 + 7 + 9 + . . . . + 139 = 4900
Therefore, 4900 is the sum of first 70 odd numbers.