Electrical Engineering - Series-Parallel Circuits - Discussion

How second parallel combination is 500 ?

Please explain.

First parallel combination of a 470 ohm resistor and a 680 ohm resistor = 277.91 ohm (w.r.t (r1*r2)/(r1+r2))
Second parallel combination of four 2 k ohm resistors = 0.5 K ohm = 500 ohm

Both first and second parallel combinations are in series to each other hence total resistance will be:
277.91 ohm + 500 ohm = 777.91 ohm i.e. 778 ohm

R1 (1st parallel comb. of 470 & 680)=333.33
R2 (2nd parallel comb. of 4 nos. of 2000) =.002
Total R (series comb. of R1 & R2) = 333.332 OHMS

Please check this with answer.

Rs=470+680=1150
Rp=8000
Req=1150*8000/1150+8000=778