15. PROBABILITY

• Finding the probability that the helicopter is crashed inside the lake

Q.) A missing helicopter is reported to have

crashed somewhere in the rectangular region

shown in fig .What is the probability that

it crashed inside the lake shown in the fig?

Sol:

Length of the rectangular region =

9 km

Breadth of the rectangular region =

4.5 km

∴ Area of the rectangular region =

9 × 4.5

Length of the lake =

9 – 6 =

3 km

Breadth of the lake =

4.5 – 2 =

2.5 km

∴ Area of the rectangular lake =

3 × 2.5

9 km

4.5 km

2 km

6 km

Lake

= 40.5 sq.km

Let A be the event that the helicopter would crashed inside the lake

Probability of event A is

–

3 km

–

2.5 km

= 7.5 sq.km

∴ P(A) =

7.5

40.5

=

P(A)

∴ P(A) =

Area of the rectangular lake = Length of the rectangular lake × Breadth of the rectangular lake

9

6

4.5

2

Area of the rectangular region = Length of the rectangular region × Breadth of the rectangular region

What is given to us?

What do we need to find?

What do we need to find?

Area of rectangular lake

Area of rectangular region

No. of favourable outcomes to event A

i.e. Area of a lake

Total no. of possible outcomes

i.e. Area of a rectangular region