Round $$398^{}\circ \rm C$$ to the nearest $$10^{}\circ $$. 
Overseas Competition->Knowledge Point->Calculation Modules->Comparing, Ordering and Estimating->Estimating Large Numbers
Rounding, $$398^{}\circ \rm C$$ is closer to $$400^{}\circ \rm C$$ than to $$390^{}\circ \rm C$$. 