Saturday 10 January 2015

A Thirst Problem



             Rajiv and Sanjiv went camping .they took their own water in big plastic bottle.
             Rajiv got thirsty and drank half the water in his bottle. A little later on he drank 1/3 of what was left. Some time afterwards he drank ¼ of what remained and so on.

          Sanjiv also had a bottle of the same size. He drank half the bottle at the first instance, half of what remained when he drank next and so on.

           After each took ten drinks the water Rajiv had left was how many times greater than the water Sanjiv had left?
Answer:  1024 / 11 times.
                                                                               R has left                                  s has left

                      End of one drink                                        ½                                             ½ 

1/11     1/2¹⁰  End of two drinks                                     1/3                                          (1/2)²

                            End of three drinks                             ¼                                             (1/2)³ 

                           End of four drinks                              1/5                                             (1/2)⁴

                           End of five drinks                               1/6                                         (1/2)⁵        
    
                           End of six drinks                                1/7                                           (1/2)⁶

2¹⁰ / 11   = 1024 / 11           end of seven drinks           1/8                                            (1/2)⁷

                                      End of eight drinks                1/9                                             (1/2)⁸

                                     End of nine drinks                   1/10                                           (1/2)⁹

                                     End of ten drinks                     1/11                                        (1/2)¹⁰

An Election Problem



    My club had a problem recently. They had to appoint a Secretary from among the men and a Joint Secretary from among the women. 

We have a membership of 12 men and 10 women. In how many ways can the selection be made?

Answer:  

 120: This problem is an example of the multiplicative principle. Here there are 12 ways of choosing the Secretary. With each of these ways it is possible to choose the Joint Secretary in 10 ways. The particular woman who is chosen as the Joint Secretary is not determined by the choice of the Secretary. The choice of each is made independently and in succession. / Therefore the total number of possibilities is the product of the two possibilities.




A Running Race



        Rajiv, Sanjiv and Vijay join a running race. The distance is 1500 metres. Rajiv beats Sanjiv by 30 metres and Vijay by 100 metres. By how much could Sanjiv beat Vijay over the full distance if they both ran as before?

Answer: 

71.4 Metres: Sanjiv runs 1470 metres while Vijay runs 1400 metres.
At the same rate Sanjiv runs 1500 metres whilst Vijay runs
1500 x 1400 / 1470 Meters
Or   1428.6 metres
Hence Sanjiv ought to beat Vijay by 71.4 metres.

Snapping a Plane



        A plane has a span of 12 metres. It was photographed as it was flying directly overhead with a camera with a depth of 12 cm.

In the photo the span of the plane was 8 mm.

Can you tell how high the plane was when it was snapped?

Answer:  
   
 180 Metres: the liner measurements of the object are to the corresponding measurements of the picture as the distance of the object from the lens is to the depth of the camera.
Let X is the height of the plane. In maters. Then we come to the following proportion:
12000:  8 = X: 0, 12
X = 180 metres
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