When the sewage of concentration Cs flow at the rate of Qs into a river stream with concentration Cr flowing at the rate of Qrthe concentration C of the resulting mixture is given by the expression?
1
= CsQs+CrQr/ QsQr+CrQ
2
= CsQs/ Qs+Qr
3
= CsQs / QsQr+CrQr
4
= CsQs+CrQr / Qs+Qr