Henry Ernest Dudeney/Modern Puzzles/163 - The Russian Motor-Cyclists

Modern Puzzles by Henry Ernest Dudeney: $163$

The Russian Motor-Cyclists

Two Russian Army motor-cyclists, on the road $A$, wish to go to $B$.

Now Pyotr said: "I shall go to $D$, which is $6$ miles, and then take the straight road to $B$, another $15$ miles.

But Sergei thought he would try the upper road by way of $C$.

Curiously enough, they found on reference to their odometers that the distance either way was exactly the same.

This being so, they ought to have been able easily to answer the General's simple question,

"How far is it from $A$ to $C$?"

it can be done in the head in a few moments, if you only know how.

Can the reader state correctly the distance?

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Unicursal and Route Problems: $163$. -- The Russian Motor-Cyclists
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Geometrical Problems: Triangle, Square & Other Polygon Puzzles: $281$. The Russian Motorcyclists