Exams

we know that speed = distance traveled/time taken
let the total distance traveled by the car is 2x km.
then time taken by it to cover first half is x/60 hour.
and for second half is x/40 hour.
Then average speed= total distance travelled / total time taken.

i.e. 2xx60+x40

=> 2x5x120

= 48 kmph.

Siphon is a tube bent to form two legs of unequal length by which a liquid can be transferred from a reservoir and then down to a lower level of it.

Siphon will fail to work if, the level of the liquid in the two vessels are at the same height.

Let the required number be 'X'

Condition 1 :  

$$\begin{gathered} XX = 2X \\ => 2X2 = X \\ => X = 12 \end{gathered}$$

Condition 2 :

$$\begin{gathered} X × X = X2 \\ => X = 12 \end{gathered}$$

Therefore, 12 is the number which becomes double when it is divided by itself and becomes half when it is multiplied by itself.

Africa is the second largest continent both by popolation and area wise. Asia being first by both popolation and area wise.

7-n = 5

Number of holidays = 2

Total number of possible ways = 9C3 = 84 ways

Required atleast one girl in the group of three = total possible ways - ways in which none is girl

None of the members in the group is girl = 6C3 = 20

Therefore, number of ways that at least one member is a girl in the group of three

= 84 - 20

= 64 ways.