42/100 as a Decimal 0.42 42/100 = 0.42 = 42% Copy 42/100 = 0.42 = 42%. Simplified: 21/50. Formula Used42 ÷ 100 = 0.42 Frequently Asked Questions What is 42/100 as a decimal?0.42.What is 42/100 as a percentage?42%.