70% Rule?

[Randy Sanchez]

I have read that the 70% rule should be applied as follows before making an offer.

Example:

$100,000 ARV

minus 20% profit

minus 10% holding and closing cost, including title insurance,
four to six months interest on loan, and realtor fees

equals $70,000 (70%)

minus repair costs $15,000

minus loan points $1,500
___________________________

Purchase price $ 53,500

Is this correct and is this still applicable in today's market?