New Scientist - USA (2020-08-22)

54 | New Scientist | 22 August 2020

Puzzle

set by Rob Eastaway

#73 Changing guard

Fifteen members of the King’s

99th Dragoons are standing on

parade. “Right turn!” screams the

sergeant, and each soldier makes

a 90° turn. Unfortunately, many

of the squad struggle to know

their left from their right. After

this manoeuvre, five soldiers

end up facing left, including

Private Perkins, who is in the

middle of the row.

X X X X X X X P X X X X X X X

Any soldier that ends up face to

face with another soldier now

does a 180° turn. This awkward

ritual continues until no soldier

can see another soldier’s face.

Can we be sure that Perkins will

end up facing the right way?

Answer next week

#72 A long lane

Solution

Professor Lemma would need

to move to number 756.

If Numero’s house number is N

and Lemma’s is L, we are told

that N x L = k x (L + N), where k

is a whole number.

With a bit of rearranging

we get: L = kN ÷ (N - k)

We want L to be as large as

possible, and therefore N - k must

be as small as possible, i.e. N - k = 1.

So k = N - 1, and hence L = (N - 1) x N.

If N = 28, L = 756.

Quick

quiz #65

Answers

1 That it was

extraordinarily

sweet; it was

sucralose, which

is now used as an

artificial sweetener

2 Pulsars. The

scruff was the fast,

repeating signals of

these rapidly rotating

neutron stars

3 Velcro

4 Kevlar

5 Thomas Edison’s

Twisteddoodles

for New Scientist

Tom Gauld

for New Scientist

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