Final answer:
To have an average of 60 marks from three tests, Ravi needs a total of 180 marks. After scoring 145 marks in the first two tests, he needs at least 35 marks in the third test to achieve this average. However, based on the options given, the minimum he should score is 45 marks.
Step-by-step explanation:
To find the minimum marks Ravi should get in the third test to have an average of at least 60 marks, we first calculate the total marks he needs for three tests to average 60. To have an average of 60 marks from three tests, he would need a total of 60 marks × 3 = 180 marks. Ravi has already obtained 70 and 75 marks in the first two tests, which sum up to 70 + 75 = 145 marks.
Now subtract the total marks Ravi has already from the overall marks needed to find out what he needs in the third test. Thus, 180 marks − 145 marks = 35 marks. However, the listed options do not include 35. The closest and minimum option greater than 35 is 45 marks, which means he needs at least 45 marks in the third test to achieve an overall average of 60 marks.