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Two pumps, A and B, are responsible for supplying water to a town. The probability that pump A fails is 0.1, and the probability that pump B fails is 0.2. The pumps operate independently. Calculate: a

Mathematics

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Answers

4 parts
a
0.72
b
0.02
c
0.26
d
0.98

Step-by-step solution

9 steps

Here's the solution for question 5:

Let P(Af)P(A_f) be the probability that pump A fails, and P(Bf)P(B_f) be the probability that pump B fails.
Given:
P(Af)=0.1P(A_f) = 0.1
P(Bf)=0.2P(B_f) = 0.2

The probability that pump A is working, P(Aw)P(A_w), is 1−P(Af)1 - P(A_f).
P(Aw)=1−0.1=0.9P(A_w) = 1 - 0.1 = 0.9

The probability that pump B is working, P(Bw)P(B_w), is 1−P(Bf)1 - P(B_f).
P(Bw)=1−0.2=0.8P(B_w) = 1 - 0.2 = 0.8

Since the pumps operate independently, we can multiply their probabilities.

Part a· 2 steps

Calculate the probability that both pumps are working.

  1. Identify the event as pump A working AND pump B working.

  2. Multiply the probabilities of each pump working.

    P(both pumps working)=P(Aw)×P(Bw)P(\text{both pumps working}) = P(A_w) \times P(B_w) P(both pumps working)=0.9×0.8P(\text{both pumps working}) = 0.9 \times 0.8 P(both pumps working)=0.72P(\text{both pumps working}) = 0.72

    The probability that both pumps are working is 0.72\boxed{0.72}.

Part b0.02

Calculate the probability that there is no water in the town.

  1. No water in the town means both pumps A and B have failed.

  2. Multiply the probabilities of each pump failing.

    P(no water)=P(Af)×P(Bf)P(\text{no water}) = P(A_f) \times P(B_f) P(no water)=0.1×0.2P(\text{no water}) = 0.1 \times 0.2 P(no water)=0.02P(\text{no water}) = 0.02

    The probability that there is no water in the town is 0.02\boxed{0.02}.

Part c0.26

Calculate the probability that only one pump is working.

  1. This can happen in two mutually exclusive ways

    • Pump A is working AND pump B is failing.
    • Pump A is failing AND pump B is working.
  2. Calculate the probability for each case.

    • P(Aw and Bf)=P(Aw)×P(Bf)=0.9×0.2=0.18P(A_w \text{ and } B_f) = P(A_w) \times P(B_f) = 0.9 \times 0.2 = 0.18
    • P(Af and Bw)=P(Af)×P(Bw)=0.1×0.8=0.08P(A_f \text{ and } B_w) = P(A_f) \times P(B_w) = 0.1 \times 0.8 = 0.08
  3. Add the probabilities of these two cases.

    P(only one pump working)=P(Aw and Bf)+P(Af and Bw)P(\text{only one pump working}) = P(A_w \text{ and } B_f) + P(A_f \text{ and } B_w) P(only one pump working)=0.18+0.08P(\text{only one pump working}) = 0.18 + 0.08 P(only one pump working)=0.26P(\text{only one pump working}) = 0.26

    The probability that only one pump is working is 0.26\boxed{0.26}.

Part d0.98

Calculate the probability that there is some water in the town.

  1. "Some water in the town" means at least one pump is working.

    This is the complement of "no water in the town".

  2. Use the complement rule

    P(some water)=1−P(no water)P(\text{some water}) = 1 - P(\text{no water}).

    P(some water)=1−P(Af and Bf)P(\text{some water}) = 1 - P(A_f \text{ and } B_f) P(some water)=1−0.02P(\text{some water}) = 1 - 0.02 P(some water)=0.98P(\text{some water}) = 0.98

    Alternatively, we can sum the probabilities of the cases where at least one pump is working:
    P(some water)=P(both working)+P(only A working)+P(only B working)P(\text{some water}) = P(\text{both working}) + P(\text{only A working}) + P(\text{only B working})
    P(some water)=P(both working)+P(Aw and Bf)+P(Af and Bw)P(\text{some water}) = P(\text{both working}) + P(A_w \text{ and } B_f) + P(A_f \text{ and } B_w)
    P(some water)=0.72+0.18+0.08P(\text{some water}) = 0.72 + 0.18 + 0.08
    P(some water)=0.98P(\text{some water}) = 0.98
    The probability that there is some water in the town is 0.98\boxed{0.98}.

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