Can you solve the death race riddle? - Alex Gendler

The night before the Death Race across
the Wastelands is set to begin,

your uncle, the great
inventor Slate Kanoli,

got kidnapped by the ruthless
No-Side gang.

The only way to get him back is to race
his Coil Runner against the gang yourself.

Win and they’ll give back your uncle.

Lose and you’ll forfeit the Coil Runner
and all his other creations.

As the grueling race gets underway,

you find yourself falling further and
further behind.

Your only chance is to take a shortcut
your uncle told you about –

the Flux Ravine gambit.

Fortunately, the Coil Runner comes
equipped with emergency turbo thrusters.

Unfortunately, your uncle was a notorious
tinkerer,

and the system still had some kinks to
work out.

Just minor things like the
ignition exploding,

the reactor leaking, or the oxygen
levels depleting––

any of which would end your racing
career immediately.

Before his kidnapping, Uncle Slate
determined that

each of these critical failures was
the ultimate result of a chain reaction

originating in the thrusters.

He was also certain that while one factor
could trigger two different effects,

and two factors could each independently
lead to the same effect,

no effect is caused by two factors
in conjunction.

However, Uncle Slate never got around
to pinpointing

which thruster was responsible for
which error.

All you have are the notes
from his test runs:

1. When thrusters B and C are on,
the Fuel gauge glows

2. When thrusters A, B, and D are on,

the Fuel gauge glows and the
Helium tank rattles.

3. When thrusters C, D, and E are on,

the Fuel gauge glows and the
Gravitometer spins

4. When thrusters A, D, and E are on,

the Gravitometer spins and the
Helium tank rattles.

5. Shortly after the Helium tank rattles
and the Gravitometer spins,

the Ignition explodes and the
Oxygen levels deplete.

6. Shortly after the Fuel gauge glows
and the Gravitometer spins,

the Reactor leaks.

You need to use as many thrusters as
possible

to give yourself the best chance at
clearing the gap,

without triggering any of the three
catastrophic failures.

Which thrusters should you activate?

Answer in 3

Answer in 2

Answer in 1

The most important thing to remember
here

is that even if we know that one
thing causes another,

the converse is not necessarily true.

For example, this panic switch shuts
off the coil runner’s engine.

But the engine being off doesn’t
necessarily mean

the panic switch was engaged––

the coil runner could be out
of fuel, or damaged––

or turned off normally.

We can, however, conclude that if the
engine is running,

the panic switch hasn’t been engaged.

With that in mind, one way we can start is
to work backwards

from the three defects that could knock
you out of the race.

So let’s look at Slate’s last two notes,

since they give direct information
about those.

The Gravitometer spins in both cases,
but the results are different.

That means the spinning Gravitometer

can’t be the cause of any
particular malfunction.

If it were, the same thing would happen
each time.

So we can conclude that a glowing
Fuel gauge makes the reactor leak,

while a rattling Helium tank makes
the Ignition explode

and depletes the Oxygen levels.

Once we know which two errors we
need to avoid, we can make a table

and use the logic of cause and effect
to see which thrusters trigger them.

Since the Helium tank is fine during the
first test run

when thrusters B and C are active,

we can assume neither makes it rattle.

And from the third run we know that
D and E don’t either.

That leaves thruster A, which was indeed
used in the second and fourth test runs

where the Helium tank rattled.

Now what causes the glowing Fuel gauge?

From the fourth test run we know it
can’t be thrusters A, D, or E.

So is the culprit, B, C, or each of them
separately?

The answer can be found in the second
and third test runs:

the fuel tank glowed in both, but B
was activated in one, and C in the other.

That means the B and C thrusters each
independently make the Fuel tank glow.

It looks like the A, B, and C
thrusters are off limits.

Fortunately, the other two are just
enough to clear the jump.

You rocket into first place and the gang
begrudgingly hands over your uncle.

He thanks you profusely, and decides
to celebrate your victory

with a cup of tea from his
latest contraption...