What is the resistance (in Ohms) of two 20 Ohm resisters in parallel?

1/20 + 1/20 = 1/R2/20 = 1/R1/10 = 1/RR = 10
Now, answer for a 20 Ohm and a 10 Ohm resister in parallel?1/20 + 1/10 = 1/R3/20 = 1/RR = 6.67 Ohm