Step 1

\(\displaystyle{31.5}\times{21.68}={682.92}\)

We know that \(\displaystyle{3}\times{2}={6}\)

Also, \(\displaystyle{30}\times{20}={600}\)

Thus solution should be \(\displaystyle{>}{600}\).

Step 2

Also, 8 (which is the last decimal digit of 21.68) \(\displaystyle\times{5}\) (which is the last decimal digit of 31.5) \(\displaystyle={40}\). This 0 cancels the 3rd decimal digit in the answer. Thus, the solution has 2 decimal digits.

\(\displaystyle{31.5}\times{21.68}={682.92}\)

We know that \(\displaystyle{3}\times{2}={6}\)

Also, \(\displaystyle{30}\times{20}={600}\)

Thus solution should be \(\displaystyle{>}{600}\).

Step 2

Also, 8 (which is the last decimal digit of 21.68) \(\displaystyle\times{5}\) (which is the last decimal digit of 31.5) \(\displaystyle={40}\). This 0 cancels the 3rd decimal digit in the answer. Thus, the solution has 2 decimal digits.