Percentage based on another column, with group by

Question

This is what I have:

create table Test(day int, status varchar(50), transactions int);
insert into Test(day, status, transactions) values(5, "success", 105);
insert into Test(day, status, transactions) values(5, "success", 105);
insert into Test(day, status, transactions) values(5, "failure", 40);
insert into Test(day, status, transactions) values(6, "success", 40);
insert into Test(day, status, transactions) values(6, "failure", 32);
insert into Test(day, status, transactions) values(7, "success", 552);
insert into Test(day, status, transactions) values(7, "failure", 4);

select day, status, sum(transactions) from Test
group by day, status

getting this one:

day status  sum(transactions)
5   success 210
5   failure 40
6   success 40
6   failure 32
7   success 552
7   failure 4

I want to have additional column, telling me per day how much is my success rate. E.g. 210/(210+40) for day 5, 40/(32+40) for day 6 etc:

day status  sum(transactions)   rate
5   success 210                 0.8400
5   failure 40                  0.1600
6   success 40                  0.5556
6   failure 32                  0.4444
7   success 552                 0.9928
7   failure 4                   0.0072