запишите обыкновенную дробь в виде десятичной дроби, разделив числитель дроби на ее знаменатель уголком:
1/4=
1/8=
3/8=
1/5=

3/4=

1\4=0.25                                                                                                                    1\8=0.125                                                                                                                  3\8=0.375                                                                                                                  1\5=0.2                                                                                                                      3\4=0.75