Answer :

610-187 is 423 but when you estimate it would be 400 this is your answer

⇒We have to estimate the difference

=610 - 187

Actual Estimation= 423

⇒Estimation using Tens

=610 - 190

= 420

⇒Estimation using Hundreds

=600 - 200

= 400

Correct estimation is

Estimation using Tens=420