Question A – Logic

In the town Gridly, the roads make a lovely square grid and one person lives at the intersection of two roads. The peaceful town was disturbed by a returned traveller who was infected with a strange disease. The disease is very infectious, but the germ only travels by road. Anyone who was infected with the disease will pass it onto the four people around it after a day. Unfortunately, only one person in this town was vaccinated (it is certainly not a smart town) and escaped the plague. After three days, almost everyone was infected, as illustrated in the graph above (the red dots are people infected).

Who got infected first?

Below is an example of how the disease might spread.

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Day 0: Initial infection
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Day 1: How infection spreads

Answer: B3


Question B – CS

Alice, Bob and Charlie are invited to a party. However, they still haven’t decided whether they will go to the party or not. If Alice goes then Bob will also go; if Alice and Bob both go, then Charlie will not go. Which of the following is/are possible situations? 

i. Only Alice and Bob go
ii. Only Alice and Charlie go
iii. Only Bob and Charlie go

A. i only
B. ii only
C. i and iii only
D. ii and iii only

Answer: C