Can You Outsmart Granny?
Three puzzles. No hints. No hand-holding.
1. Granny’s Brothers and Sisters
Granny grew up in a big family and was hoping to have many children of her own.
She has as many brothers as she has sisters.
Each of her brothers has only half as many brothers as sisters.
Question:
How many brothers and sisters are in Granny’s family?
2. Sirius’ Stopped Clock
The clock in Sirius' shrine stopped working years ago, at exactly the same moment his heart did. Granny leaves it that way as a memory of her dear late husband.
The minutes that had already passed in that hour were five times the number on the hour hand, and the minutes still left before the next hour were also five times the number on the hour hand.
Question:
At what time did Sirius pass away?
3. Granny’s Corridor Trap
In Granny’s house there is a 24 metre corridor with a door at each end. Along the walls are 5 lamps, evenly spaced between the doors.
Granny has installed a tennis ball machine at one end. When she presses the big red button next to her bed, the machine takes 3 seconds to fire, and when it does, the balls fly so fast that anyone still in the corridor is guaranteed to be hit.
She watches the corridor on her Ring camera, but the video is always 1 second behind real time. Intruders tend to walk at a steady 1 m/s and run four times faster.
Granny has worked out a rule:
“If I press the button when they are standing next to a certain one of the five lamps, they are guaranteed to be hit by the ball, whatever direction they run.”
Question:
Which lamp is Granny's special marker?
No spoilers in the room, promise. Probably.