>>syms y t
>>int(exp((y-221)^2/2/t^2),0,200)
ans =
(2^(1/2)*pi^(1/2)*t^2*(erf(21*(-1/(2*t^2))^(1/2)) - erf(221*(-1/2/t^2)^(1/2)))*(-1/t^2)^(1/2))/2
>>solve('(2^(1/2)*pi^(1/2)*t^2*(erf(21*(-1/(2*t^2))^(1/2)) - erf(221*(-1/2/t^2)^(1/2)))*(-1/t^2)^(1/2))/2=sqrt(2*pi)*t*0.1')
ans =
808.96570511067102425235829152553