Two congruent circles have centres at O and $O^{\prime}$. Arc AXB of circle centred at O, subtends an angle of $75^{\circ}$ at the centre O and arc PYQ (or circle centred at $O^{\prime}$) subtends an angle of $25^{\circ}$ at the centre $O^{\prime}$). The ratio of the arcs AXB and PYQ is __________.
Two chords AB and AC of a circle are on the opposite sides of the centre. If AB and AC subtend angles equal to $90^{\circ}$ and $150^{\circ}$ respectively at the centre, then $\angle B A C$ = __________.
ABCD is such a quadrilateral that A is the centre of the circle passing through B, C and D. If $\angle C B D+\angle C D B=k \angle B A D$, then k = __________.
ABCD is a cyclic quadrilateral such that AB is a diameter of the circle circumscribing it and $\angle A D C=140^{\circ}$, then $\angle B A C=$ __________.