create table #dt
(
	id		int,
	timeinmins	nvarchar(10)	-- Actually your time is not in minutes but <minutes>.<seconds>
)

insert into #dt
select	1, '1.20'	union all
select	2, '1.40'	union all
select  1, '2.30'	union all
select  1, '0.10'	union all
select  3, '0.3'

select	id, cast((tm_secs / 60) as int) as tm_min, tm_secs % 60 as tm_sec,
	convert(varchar(2), cast((tm_secs / 60) as int)) + '.' + convert(varchar(2), tm_secs % 60) as tm_in_string
from
(
	-- convert from <minutes>.<seconds> to <total seconds>
	select	id, cast(sum((cast(tm_num as int) * 60) + ((tm_num - cast(tm_num as int)) * 100)) as int) as tm_secs
	from
	(	
		-- convert the timeinmins from nvarchar to numeric(6,2) for ease of processing
		select	id, cast(timeinmins as numeric(6,2)) as tm_num
		from	#dt
	) as dt_num
	group by id
) as dt_in_secs

drop table #dt