A finance manager is considering drilling a well on their property. Based on past data, there is a 70% chance of finding water at 20 meters depth, and a 20% chance of finding water between 20-25 meters if no water is found at 20 meters. The costs to drill are Rs.500 per meter plus Rs.15,000 to buy water externally if the well is not drilled. The optimal decision tree strategy is to first drill to 20 meters, and if no water, then drill further to 25 meters, resulting in an expected cost of Rs. 11,350.

1. Decision Tree
Decision Theory

2. A finance manager is considering drilling a well. In the past, only 70% of
wells drilled were successful at 20 metres depth in that area. Moreover, on
finding no water at 20 metres, some persons in that area drilled in further
up to 25 metres but only 20% struck water at that level. The prevailing cost
of drilling is Rs.500 per metre. The finance manager estimated that in case
he does not get water in his own well, he will have to pay Rs.15000 to buy
water from outside for the same period of getting water from the well. The
following decisions are considered:
i. Do not drill the well,
ii. Drill up to 20 metres, and
iii. If no water is found at 20 metres, drill further up to 25 metres.
Draw an appropriate decision tree and determine the finance manager’s
optimum strategy.
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3. Decision Tree

4. D1
C1
D2
C2
do not drill
drill up to 20m
water found
no water found
do not drill
drill up to 25m
water found
no water found
p = 0.7
p = 0.3
p = 0.2
p = 0.8
-15000
-15000
-17500
-2500
-10000
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5. Roll-Back

6. D1
C1
D2
C2
do not drill
drill up to 20m
water found
no water found
do not drill
drill up to 25m
water found
no water found
p = 0.7
p = 0.3
p = 0.2
p = 0.8
-15000
-15000
-17500
-2500
-10000
-14500
-11350
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7. 𝑨𝒏𝒔: 𝑫𝒓𝒊𝒍𝒍 𝒖𝒑𝒕𝒐 𝟐𝟎𝒎, 𝒊𝒇 𝒏𝒐 𝒘𝒂𝒕𝒆𝒓, 𝒅𝒓𝒊𝒍𝒍 𝒖𝒑𝒕𝒐 𝟐𝟓𝒎. 𝑬𝒙𝒑𝒆𝒄𝒕𝒆𝒅 𝒄𝒐𝒔𝒕: 𝑹𝒔. 𝟏𝟏𝟑𝟓𝟎
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