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According to the Central Statistics Office (CSO) there were 65 909 babies born in Ireland in 2015 - Leaving Cert Mathematics - Question 1 - 2017

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According to the Central Statistics Office (CSO) there were 65 909 babies born in Ireland in 2015. Of these 32 290 were girls. (a) (i) How many boys were born in Ir... show full transcript

Worked Solution & Example Answer:According to the Central Statistics Office (CSO) there were 65 909 babies born in Ireland in 2015 - Leaving Cert Mathematics - Question 1 - 2017

Step 1

How many boys were born in Ireland in 2015?

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Answer

To find the number of boys born in Ireland in 2015, we subtract the number of girls from the total number of babies:

65,90932,290=33,61965,909 - 32,290 = 33,619

Thus, there were 33,619 boys born in Ireland in 2015.

Step 2

Find the probability that a baby picked at random from those born in Ireland in 2015 is a boy.

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Answer

The probability P(B)P(B) that a randomly selected baby is a boy can be calculated using the formula:

P(B)=Number of boysTotal number of babiesP(B) = \frac{\text{Number of boys}}{\text{Total number of babies}}

Substituting the values:

P(B)=33,61965,9090.51P(B) = \frac{33,619}{65,909} \approx 0.51

Thus, the probability is approximately 0.51 when rounded to 2 decimal places.

Step 3

Use your answer to part (a)(ii) to find the probability that the first three babies born were boys.

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Answer

The probability that the first three babies born were boys can be found by raising the probability of a boy to the power of 3:

P(3 boys)=(0.51)30.132651P(3 \text{ boys}) = (0.51)^3 \approx 0.132651

Thus, the probability is approximately 0.1327 when rounded to 4 decimal places.

Step 4

Find the probability that the third birth was the first girl born in the hospital that day.

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Answer

To find this probability, we consider that the first two births must be boys and the third must be a girl. This is calculated as:

P(2 boys, 1 girl)=(0.51)(0.51)(10.51)=(0.51)2(0.49)0.127449P(2 \text{ boys, 1 girl}) = (0.51)(0.51)(1-0.51) = (0.51)^2(0.49) \approx 0.127449

Thus, the probability is approximately 0.1275 when rounded to 4 decimal places.

Step 5

Complete the table.

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Answer

To complete the table, we need to ensure that the sum of probabilities equals 1. Adding the given probabilities:

0.14+0.15+0.18+0.15+0.12+0.1=0.840.14 + 0.15 + 0.18 + 0.15 + 0.12 + 0.1 = 0.84

Thus, the probability for Sunday is:

10.84=0.161 - 0.84 = 0.16

The completed table will include Sunday with a probability of 0.16.

Step 6

Find the number of babies expected to be born on the Tuesday of that week.

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Answer

To find the expected number of babies born on Tuesday, multiply the total number of babies born by the probability for Tuesday:

Expected=1300×0.15=195Expected = 1300 \times 0.15 = 195

Therefore, the expected number of babies born on Tuesday is 195.

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