4/10 as a Decimal 0.4 4/10 = 0.4 = 40% Copy 4/10 = 0.4 = 40%. Simplified: 2/5. Formula Used4 ÷ 10 = 0.4 Frequently Asked Questions What is 4/10 as a decimal?0.4.What is 4/10 as a percentage?40%.