Question

which way ill spend more money, by gibing compensation to worker per mounth or per week? (a little trick)

Answer 1

you will spend more money if you pay a worker per week. when you pay a worker at the end of each 4-week period you have gained interest on the money you did not pay fro weeks 1, 2 and 3.
On the first weeks payment you loose 3 weeks interest, on the second weeks payment you would loose 2 weeks interest and on the third weeks payment you loose one weeks interest. The last week has no loss of interest because you would pay that amount of money in each scenario.
For bonus points you could add calculating what a bonus remuneration would do for you in terms of delayed payment vs. higher salary. To exemplify: pay your worker $400 per week vs. $1720 per month vs. $1500 per month with a yearly bonus of $2640.

Answer 2

well its just, 1 mouth=4 weeks,1year = 52 weeks, 52/4 = near to 13 mounths, ^^