Practice GMAT Problem Solving Question
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A coin has two sides. One side has the number 1 on it and the other side has the number 2 on it. If the coin is flipped three times what is the probability that the sum of the numbers on the landing side of the coin will be greater than 4?
Correct Answer: D
- One approach to solve the problem is to list the different possibilities for a toss of coin three times. Because there are two outcomes and the coin is tossed three times, the table will have 2*2*2 or 8 rows.
- Next add the resulting rows together to find the sum (the fourth column in the table below).
| Toss 1 |
Toss 2 |
Toss 3 |
Sum |
| 1 |
1 |
1 |
3 |
| 1 |
1 |
2 |
4 |
| 1 |
2 |
1 |
4 |
| 1 |
2 |
2 |
5 |
| 2 |
1 |
1 |
4 |
| 2 |
1 |
2 |
5 |
| 2 |
2 |
1 |
5 |
| 2 |
2 |
2 |
6 |
- From the table we see that there are 4 situations where the sum of the tosses will be greater than 4. And there are 8 possible combinations resulting in a probability of
- 4/8 or a probability of1/2. SO the correct answer is D.
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