Which one of the two , an ammeter or a milliammeter, has a higher resistance and why?

Explanation

To convert a galvanometer into an ammeter of range I we join a shunt resistance `r_s` given by
`r_s = (I_g)/(I - I_g) cdot R_G`
and then net resistance of ammeter is `(r_s . R_G)/(r_s + R_G),` which is slightly less than even `r_s`.
As range l of an ammeter is more than that of a milliammeter, hence value of shunt resistance is lesser for an ammeter. Consequently, resistance of an ammeter is less or comparatively speaking resistance of a milliammeter is higher.