One dollar equals one pound worth of rubles. As I remember, this joke was made in the 1990s due to the ruble’s current slide. The ruble had a much lower value than it does now. Wikipedia says that the exchange rate of the ruble against the U.S. Dollar declined from $1 =125 RUR in January 1992, to $1 = 6,096 RUR by 1998, when the currency was redenominated.