Switch-a-roo

In the circuit above, $R_1 = \SI[per-mode=symbol]{10}{\ohm}$ , $R_2 = R_3 = \SI[per-mode=symbol]{30}{\ohm}$ , $R_4 = \SI[per-mode=symbol]{40}{\ohm}$ and the equivalent resistance between points $A$ and $B$ is $X$ ohms. If the ammeter and the voltmeter are switched, the equivalent resistance between points $A$ and $B$ now is $Y$ ohms. What is $X+Y$ ?

(Assuming that the ammeter and voltmeter are ideal.)