Question

twice a number minus 4 is less than three times number

Answer 1

2x - 4 < 3x

Just follow the question.

Answer 2

Let the number be x
twice a number: 2x 
minus 4: -4
three times a number: 3x
less than symbol: <

form the equation exactly how the sentence is written to give:
2x - 4 < 3x

rearrange by taking 2x away from each side to give an expression for x:
-4<x