Last Updated on May 3, 2023
GMAT OFFICIAL GUIDE PS
Solution:
We can solve this problem in a similar manner to solving a work problem, and we can use a table to organize our information. We can fill in what she was “supposed” to do and what she “did” do.
We are given that her initial plan was to read 90 pages per day for “T” days. We can multiply, getting 90T for the total work that was supposed to be done for the entire reading assignment.
We are next told that she actually started out reading 75 pages per day until she had 6 days left to finish the project. Since T represents the total number of days we can say she read 75 pages per day for (T–6) days. Finally, when we multiply, we see that her work done on the T–6 days was 75T–450.
| Rate | Time | Work | |
|---|---|---|---|
| Supposed | 90 | T | 90T |
| Did | 75 | T − 6 | 75(T − 6) = 75T − 450 |
To finish this problem we need to set up one final equation. We are told that she must read 690 pages in the last 6 days to complete the assignment. From the chart we see that 90T denotes a completed assignment. Thus we can say:
75T – 450 + 690 = 90T
75T + 240 = 90T
15T = 240
T = 16
Answer: B
