Ex4 22

$\def\abs#1{|#1|}\def\i{\mathbf {i}}\def\ket#1{|{#1}\rangle}\def\bra#1{\langle{#1}|}\def\braket#1#2{\langle{#1}|{#2}\rangle}\def\tr{\mathord{\mbox{tr}}}\mathbf{Exercise\ 4.22}$

Show that no matter in which basis the first qubit of an EPR pair $\frac{1}{2}(\ket{00} + \ket{11})$ is measured, the two possible outcomes have equal probability.