Variance of equally weighted portfolo question question, equation, standard

Bluetick1010

Suppose .3 is the common correlation of returns between any two stocks in a portfolio containing 100 stocks. Also, suppose the average variance of stocks in the portfolio is 625 (corresponding to a standard deviation of return of 25%). Calculate the portfolio standard deviation.
A: .0625 [(1 - .3 / 100) + .3] = .01919, square root = 13.852%
Is there anyway to find this answer using the equation that utilizes covariance:
1/n*avg. variance of all assets in the portfolio + n - 1 / n*avg. covariance of all pairings of assets in the portfolio
I assume there is since the equation they used to solve the problem is derived from the second one I wrote.

Benjiko

Var(p)= 191.875
= 1/100*625 + 99/100*0.3*625
std dev=sqrt(191.875) = 13.852
same answer.