Please help on this maths arithmetic problem

Question

The set of odd numbers are arranged as follows:

1

3 5 7

9 11 13 15 17

19 21 23 25 27 29 31

1. What is the middle number of the 20^th row?

Answer 1

the number av odd numbers in eech roe=1, 3, 5, 7,...=the odd numbers

thru roe 19, yu du 361 odd numbers...sum av first 19 odd numbers

so roe 20 start with the odd number 362

that odd num is 1+2*(n-1)=1+2*361=723

num numbers in roe 20=2*19+1=39

roe 20...723, 725, 727, 729, 731...

middel= 20 akrost & 20th tern av roe 20 is 761