Thomas is remaining track of the rainfall in the month of May for his science project. The first day, 2.6 cm of rain fell. On the second day, 3.4 cm fell. On the third day, 2.1 cm fell. How many more cm are required to reach the average monthly rainfall in May, that is 9.7 cm?
Find out the amount of rain in which has fallen so far; 2.6 + 3.4 + 2.1 = 8.1 cm. Find out the difference among this amount and the average rainfall through subtracting; 9.7 - 8.1 = 1.6 cm.