Which should i do first - yoga or exercise?

to reduce weight i m doing both
which should i do first and which later?

do both.

It depends on the type of yoga and how you feel/time of the day.

I do excercise, sweat it all out then take a shower and do a hatha yoga class which is quite a basic mild yoga class.

If there is an ashtanga class I do a workout before and then a toneing /body conditioning class after.

I do think it varies from class to class and teacher to teacher, some yoga classes are intense and make you sweat (ashtanga, bikrum, vinyasa and some iyengar classes) and some will calm you down (pure yoga, hatha, anusara, pranayama and some iyengar) ask the teachers.

Most if not all classes begin and end with yopu being in the corpse pose, thats a relaxation pose and this could calm you down after a heavy bout of excercise which is why I generally tend to do it afterwards. Sometimes its not possible though and I would recommend choosing a more cardio type of yoga before a workout.

I did the same when I was trying to lose weight, I did weights, swimming and cycling and yoga, one of each a week, on diferent days, an hour of yoga is actually hard work and I would only recommend a swim after. Good luck.

do cardio for 20-25 mins,then yoga for 45-90 mins and finally another session of cardio for 20-25 mins 5 or 6 times a week

cardio exercise is the base for all other activities but nothing wrong in doing a hatha yoga class for relaxation once a week, say on a sunday at the gym?

Yoga to stretch and warm up first, then exercise or yoga one day and exercise the next.

exercise first then yoga to relax the muscles and lower your heart rate

Excercise meant for youth and yoga for old. If you combine both it is good.

Exercise such as cardio, get ur heart rate up, then do yoga.