The container `A` is constantly maintained at `100^(@)C` and insulated container `B` in the contains ice at `0^(@)C` Different rods are used to connect them For a rod made of copper, it takes 30 mintes for the ice to melt and for a rod of steel of same cross-section taken in different experiment it takes 60 minutes for ice to melt. When these rods are simultaneously connected in parallel, the ice melts is
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Explanation

`Q=` it where `i=` heat flows rate `=(DeltaT)/(R )=(100)/(R )`
For copper rod :
`Q=((100)/(R_(1)))(30)implies R_(1)=((100)/(Q))xx30`
Also for steel rod :
`Q=((100)/(R_(2)))xx60implies R_(2)=((100)/(Q)xx60`
Now, `Q=((1)/(R_(1))+(1)/(R_(2)))t_(reqd.)`
`:. t_(reqd)=(Q)/(((Q)/(100))xx(1)/(30)+((Q)/(100))xx(1)/(60))=20min`