You measure two quantities as A=1.0m±0.2m,  B=0.2m±0.2m. We should report correct value for AB is

Given A=1.0  m±0.2  mB=2.0  m±0.2  mx=AB=1.0×2.0=1.414  mRounding-off to two significant digits,x=AB=1.4  mNow, Δxx=12[ΔAA+ΔBB]=12[0.21.0+0.20.2]=0.62×2.0Δx=0.6×x2×2.0=0.15×1.414=0.2121Rounding-off to one significant digits, Δx=0.2  mThus, AB=1.4 m±0.2 m