Question

what is the highest and the lowest total resistance which can be secured by combination of 4 coils of resistance 4 ohm 8 ohm 12 ohm and 24 Ohm

Answer 1

highest= 48 ohms
lowest=2 ohms

for highest total resistance, connect in series:
R=4+8+12+24
R=48 ohms

for lowest total resistance connect in parallel:
1/R=1/4+1/8+1/12+1/24
1/R=1/2
R=2 ohms