On 1 October 2019, Mr Han received a notice of original assessment showing tax payable of $1,000 for the Year of Assessment 2019. According to his own calculation, the amount of tax payable should only be $900. He wanted to send a cheque for $900 to IRAS on 29 October 2019, but decided to seek your advice first.

Required:

(a) How would you advise him?

(b) Briefly explain what would happen if he had proceeded to send a cheque for $900 to IRAS on 29 October 2019 with no further follow up action.