A 6 ohm resistance wire is doubled up by folding. calculate the new resistance of the wire.

resistance is given as

R = ρl/A

where 

ρ is the resistivity (stays constant)

l is the length

A is the cross-sectional area

now initially R = 8 ohms

but if we fold the wire on itself then

A' = 2A

l' = l/2

so, new resistance

R' = ρl'/A' = ρl/2/2A

or

R' = R/4

so, the new resistance will be R' = 8/4 ohms
So now new resistance = 2 ohm.