Question

it takes riaz 30 minutes to mark a paper.razi only need 25 minutes to mark a paper.if they both start marking paper at 11.00am.what is the first time they will finish marking a paper at same time

Answer 1

LCM of 30 and 25 mins = 150 mins

So, they will finish marking paper at same time at 11:00 + 150 mins
                       = 1:30 pm
                                                    

Answer 2

Taking LCM can make us to find the least time for chance of finishing at same

time.

Prime factors of 30 mins (Raiz) = 2 × 3 × 5
 
Prime factors of 25 mins (Razi) = 5 × 5

then, LCM = 2 × 3 × 5 × 5

                  = 150 mins

                  = 2 hrs 30 mins

Then the time they will finish same = 11:00 + 2:30
        
                                                        = 13:30 (railway time)
               
                                                        = (or) 1:30 p.m

☺ Hope this Helps ☺