Question

10 is 40% of what number

Answer 1

25 is the 40% of 10. 

Answer 2

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 !!