Question

1+3+5+7+9+11+13+15+17+19+21+23+25+27+29+31+33+35+37+39 without adding find their sum?


NOTE:DO NOT USE AP FORMULA

Answer 1

these are the first 20 odd terms.
so,
sum of these terms = (20)² = 400....

hope it helped

Answer 2

the sum of continuous odd numbers from 1 to 39=n²(where n is the total number of terms)
so, 20²=400

so, sum of all odd numbers from 1to 39=400