Question

Two circular bronze docs of radii 3cm and 4cm are melted down and cast into a single disc of the same thickness as before. What is the radius of the new disc
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Answer 1

Answer:

Let the thickness of the discs be t, then the volume of two discs =π(3^2+4^2)×t=π×25×t

Let the radius of the new disc be R, then it's volume=πR^2×t

πR^2t=π×25×t

R^2=25

R=5 cm