If i practice 12 mins which is 40% of the time needed how much more time do i need to practice?

Question

just need help with formula 

Answer 1

Let x = total time needed to practice

 

Translate:

  "12 mins which is 40% of the time needed"    means

    12           =      (40/100)x                ["of" means multiply]

      [note:  40% is written as (40/100) or 0.40 as needed by the problem]

 

 12 = (40/100)x

(100/40)12 = x             [multiply both sides by 100/40]

  30 = x

 

  "I practice 12 mins"

 

So, 30-12=18 minutes more practice are needed.

Answer 2

Percent equation

 

part/whole = percent/100

 

 

here 

 

part = 12

percent = 40

 whole =x

 

12 /x =40/100

 

12*100 = 40* x

 

1200=40x

 

30 = x

 

total time is 30 min

 

so you have to do = 30-12=18 min more practice