In a circle of radius 17 cm two parallel chords measure 16 cm and 30 cm, and the centre of the circle lies between them. How far apart are the two chords?

The perpendicular from the centre bisects each chord, so the distances from the centre are √$(17^2-8^2)=$ √225 = 15 cm for the 16 cm chord and √$(17^2-15^2)=$ √64 = 8 cm for the 30 cm chord. Because the centre lies BETWEEN the chords, the two distances add: 15 + 8 = 23 cm. The trap 7 cm subtracts them, which is the answer for the other arrangement, with both chords on the same side of the centre — a case worth separating carefully. The value 34 cm is the diameter and 46 cm merely adds the two chord lengths.