When a retired doctor was asked to subtract seven from 100, the octogenarian, who had dementia, answered 200.

The late Dr Freda Paul's inability to do simple arithmetic in December 2009 was cited by the High Court yesterday as a reason why it found that she lacked the mental capacity in 2010 to give away a total of $5 million to her maid, a construction worker and an engineer.

Judicial Commissioner Debbie Ong ordered construction worker Kulandaivelu Malayaperumal to return $2 million to Dr Paul's estate. Engineer Gopal Subramaniam was ordered to return about $912,000.

A default judgment had earlier been obtained against Sri Lankan maid Arulampalam Kanthimathy, who had received $2 million. She returned home in 2012.

The money came from the sale of Dr Paul's sole asset, a Haig Road bungalow that was sold in 2009 for $15.4 million.

"I do not think that Dr Paul would have had the capacity to appreciate property value and determine the distribution of sale proceeds, given her lack of arithmetic ability," said the Judicial Commissioner.

She found that the defendants had "supplied hindrances" to Dr Paul's independence in decision- making, cutting her off from her friends and relatives. She was also made to live in unclean conditions, including sleeping on newspapers spread out on the bed.

Dr Paul was a paediatrician at the Singapore General Hospital. She was single and died in August last year at the age of 87.

In the early 2000s, she befriended Mr Malayaperumal, a worker at a nearby construction site, and his supervisor, Mr Subramaniam. Both were from India.

In mid-2009, Mr Malayaperumal moved into her home.

Months later, she signed a power of attorney authorising Mr Subramaniam to sell the house and to buy a smaller one.

Before the house was sold, Dr Paul underwent a psychiatric assessment. She could not do simple arithmetic and could not recall the names of simple objects two minutes after she was told, but was certified fit to sell her house.

In 2010, Mr Subramaniam used the proceeds to pay $1 million to Mr Malayaperumal, $1 million to Ms Kanthimathy and $912,000 to himself. He used $2.4 million to buy a house in Ceylon Road for Dr Paul.

Six months later, Mr Malayaperumal and Ms Kanthimathy each received another $1 million.

Dr Paul also willed most of her assets to Mr Malayaperumal and Ms Kanthimathy, in stark contrast to her 2007 will in which she wished for the bulk of her wealth to be used to set up a bursary fund for needy female medical students at the National University of Singapore.

In 2013, her distant relatives, Senior Counsel Philip Jeyaretnam and Dr Ruhunadevi Joshua, were appointed under the Mental Capacity Act to manage her affairs.

Suspecting that she had been exploited, they went to court to reinstate the terms in the 2007 will and filed a suit to recover the money.

Yesterday, their lawyer, Mr Herman Jeremiah, said the judgment "redresses in no small way the advantage that the defendants had taken of Dr Paul's vulnerability".

A successful recovery of the judgment sums would mean more money in the bursary fund to be set up in the name of Dr Paul, he said.