The rate of inches of rain to time is 7.7:10. In fraction form, we can write it as:
Multiply both numerator and denominator by 10:
77 is equal to 7 times 11, and 100 is equal to 2^2 times 5^2. Since 77 and 100 have no prime factors in common, then their greatest common divisor is 1. So, the fraction 77/100 is already in its lowest terms.