10 is 40% of what number
25 is the 40% of 10.
let the unknown number be a ..40% of a = 10=> 40/100a = 10=> 2/5a = 10 => 2a = 10 * 5 => a = 50/2 => a = 25 so 10 is 40% of 25 ..Hope it helps !!
