pH of acid or base mixtures

Exercise 1

Determine the $pH$ of the solution obtained by mixing $V_1$ = 200 $mL$ $HBr$ 0.05 $M$ with $V_2$ = 200 $mL$ $HI$ 0.6 $M$

$HBr$ ,$ HI$ :    strong acids $n_{HBr}$ $=$ $c_{HBr}\cdot V_1$ = 0.01 $mol$ $n_{HI}$ $=$ $c_{HI}\cdot V_2$ = 0.12 $mol$ $pH$ $=$ $-log\frac{n_{HBr} + n_{HI}}{V_1+V_2}$ = 0.488