The equivalent resistance when two resistors are connected in series is
the sum of their individual resistances.
The marking on the resistor that says "1000 W" is the rating that tells
how much power the resistor can safely dissipate, without overheating
or exploding. (The 'W' stands for 'Watts'.) It doesn't tell us anything about
their individual resistances. So we don't have enough information to calculate
their series equivalent.