The correct option is B 8×108
Given:
Number of mobile phones produced in 1 day =4×105
To Find:
Number of mobile phones produced in 2,000=2×103 days.
∴ Number of mobile phones produced in 2×103 days =2×103 × Number of mobile phones produced in 1 day
=2×103×4×105
=2×4×103×105
=(2×4)×(103×105)
=8×(103×105)
Applying the multiplication rule for same base and different exponents: am×an=am+n
=8×10(3+5)
=8×108
Therefore, 8×108 mobile phones can be produced by the manufacturer in 2,000 days.
Hence, option (b.) is the correct one.