1)If 15 toys cost Rs.234, what do 35 toys cost ?

Sol:     Let the required cost be Rs. x then 
         more toys more cost(direct proportion)
          15:35:: 234:x
          (15*x)=(234*35)
              x=(234*35) /(15)= 546 Rs

2)If 36 men can do a piece of work in 25hours, in how many hours will 
   15men do it?

 Sol:     Let the required number of hours be x.
          less men more hours(Indirect proportion).
          15:36::25:x
          (15*x)=(36*25)
               x=(36*25) /15
               x=60
          For 15 men it takes 60 hours.

3)If 9 engines consume 24metric tonnes of coal, when each is working 
8 hours a day, how much coal will be required for 8 engines, each 
running 13 hours a day, it being given that 3 engines of former type 
consume as much as 4 engines of latter type?

Sol:       Let 3 engines of former type consume 1 unit in 1 hour.
               4 engines of latter type consume 1 unit in 1 hour.
           1 engine of former type consumes 1/3 unit in 1 hour.
           1 engine of latter type consumes ¼ unit in 1 hour.
           Let required consumption of coal be x units.
           Less engines, less coal consumed.(direct)
           More working hours, more coal consumed(direct)
           Less rate of consumption, less coal consumed (direct)
 
                     9:8
                     8:13            ::  24:x
                     1/3:1/4  

                   (9*8*(1/3)*x)=(8*13*(1/4)*24)

                  24x=624

                    x=26 metric tonnes.



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