Final answer:
The statement is true as 15 millimeters of rain over 12 hours equates to 1.25 millimeters per hour, which is the same as 1 whole and 1/4 millimeters.
Step-by-step explanation:
The student asks whether it is true that it rained 1 and 1/4 millimeters of rain per hour when there was a total of 15 millimeters in 12 hours. To determine the amount of rain per hour, we need to divide the total amount of rainfall by the total number of hours. Doing the calculation, 15 millimeters divided by 12 hours equals 1.25 millimeters per hour. This confirms the statement is true.
The unit rate of rain per hour is 1.25 millimeters, which is equivalent to 1 whole 1/4 millimeters. So, the correct option is true as the calculation aligns with the given value. This example uses the concept of rate from mathematics to understand a practical scenario of rainfall measurement. Comparing this to the given unit of 1 whole 1/4 millimeter of rain per hour, we can see that it is false, as the rainfall rate is 1.25 millimeters per hour, not 1 whole 1/4 millimeter.