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#177 Monkeying around

¿ìè¶ÌÊÓƵs have been studying two rare monkey species in a forest.

In one part of the forest live the Equalis monkeys, which are split 50-50 between males and females. In another part of the forest are the Fraternis monkeys, of which exactly two-thirds are male – the evolutionary aspect of this isn’t yet known.

Both species are monogamous, with families coming in all shapes and sizes. Some parents stop at one offspring, but there are others with 10 or more, so some monkeys have lots of brothers, while others have none at all. The sex of any infant is independent of others in their family.

Among Equalis monkeys, which should expect to have more brothers, the males or the females? And how about Fraternis monkeys?

Solution next week

#176 Ant-i-clockwise

Solution

The minute hand rotates 6 degrees per minute. So, during the 15 minutes of the ant’s anticlockwise walk, the hand moves 15 x 6 degrees = 90. In that time, the ant travels around 360 degrees – 90 degrees = 270 degrees of the clock face, which is 18 degrees per minute, or three times the speed of the minute hand. In the first, clockwise stage of the ant’s journey, the ant must therefore move through 300 degrees (the angle from 2 o’clock to 12 o’clock) + the angle (x) rotated by the minute hand. The ant travels at three times the speed of the minute hand, so 300 + x = 3x; x = 150 degrees, which takes the ant 25 minutes. The total journey takes 25 minutes (stage 1) plus 15 minutes (stage 2), so it stops walking at 2.40.

Answers