We have,
Total surface area of hollow cylinder = 4620 cm2
Area of base ring = 115.5 cm2
Height of cylinder = 7 cm
Let outer radius be ‘R’ cm , inner radius be ‘r’ cm
Area of hollow cylinder = 2π(R2 – r2) + 2πRh + 2πrh
= 2π(R+r)(R-r) + 2πh(R+r)
= 2π(R+r) (h+R-r)
Area of base = πR2 – πr2
= π (R2 – r2)
= π (R+r) (R-r)
Surface area / area of base = 4620/115.5
{2π(R+r) (h+R-r)} / { π (R+r) (R-r)} = 4620/115.5
2(h+R-r) / (R-r) = 4620/115.5
Let us consider (R-r) = t
2(h+t)/t = 40
2h + 2t = 40t
2h = 38t
2(7) = 38t
14 = 38t
t = 14/38
= 7/19 cm
∴ Thickness of cylinder is 7/19 cm.