At a clockmaker's shop, the purchases for one month are recorded in the table below:

| | Remodel | Repair | New Purchase |
|---------------|---------|--------|--------------|
| Watch | 73 | 47 | 19 |
| Clock | 61 | 59 | 11 |
| Alarm Clock | 83 | 41 | 17 |

If we choose a customer at random, what is the probability that they have purchased an alarm clock or a new purchase?

[tex]\[ P(\text{Alarm Clock or New Purchase}) = \frac{57}{?} \][/tex]

Give your answer in simplest form.



Answer :

To determine the probability that a randomly chosen customer has purchased an alarm clock or made a new purchase, we need to follow several steps:

1. Calculate the total number of customers:

We will sum up all the given values for each category:
- Watch: [tex]\(73 + 47 + 19 = 139\)[/tex]
- Clock: [tex]\(61 + 59 + 11 = 131\)[/tex]
- Alarm Clock: [tex]\(83 + 41 + 17 = 141\)[/tex]

So, the total number of customers is:
[tex]\[ 139 + 131 + 141 = 411 \][/tex]

2. Calculate the total number of customers who purchased an alarm clock:

Customers who purchased an alarm clock fall into all three categories (Remodel, Repair, New Purchase):
[tex]\[ 83 + 41 + 17 = 141 \][/tex]

3. Calculate the total number of customers who made a new purchase:

Customers who made a new purchase fall into each type of clock (Watch, Clock, Alarm Clock):
[tex]\[ 19 + 11 + 17 = 47 \][/tex]

4. Calculate the overlap between customers who made a new purchase and those who purchased an alarm clock:

Specifically, these are the customers who made a new purchase of an alarm clock, which is:
[tex]\[ 17 \][/tex]

5. Calculate the total number of customers who purchased an alarm clock or made a new purchase:

Since the customers who made a new purchase of an alarm clock are counted in both categories, we need to subtract this overlap once:
[tex]\[ 141 + 47 - 17 = 171 \][/tex]

6. Calculate the probability:

The number of favorable outcomes (customers who either purchased an alarm clock or made a new purchase) is [tex]\(171\)[/tex], out of a total of [tex]\(411\)[/tex] customers.

Therefore, the probability is:
[tex]\[ P(\text{Alarm Clock or New Purchase}) = \frac{171}{411} \][/tex]

7. Simplify the fraction to its simplest form:

Both [tex]\(171\)[/tex] and [tex]\(411\)[/tex] can be simplified by finding their greatest common divisor (GCD). The GCD of [tex]\(171\)[/tex] and [tex]\(411\)[/tex] is [tex]\(3\)[/tex]. So, we simplify the fraction:
[tex]\[ \frac{171 \div 3}{411 \div 3} = \frac{57}{137} \][/tex]

Thus, the probability that a randomly chosen customer has purchased an alarm clock or made a new purchase is:
[tex]\[ P(\text{Alarm Clock or New Purchase}) = \frac{57}{137} \][/tex]

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