75% of 420

Since 75% is the same as 0.75 (< the decimal form), simply multiply 420 by 0.75.

$${\mathtt{420}}{\mathtt{\,\times\,}}{\mathtt{0.75}} = {\mathtt{315}}$$

let us do it like this ;

as 100 is the  whole percen so 

75/100 x 420

cut  100 and 420 by 100 being 5 and 420 being 21 .

75/5 x 21

cut 75 by 5 with 75 being 15 

so now u have

15 x 21

=315

so 75 percent of 420 is 315 !