A five-digit number is called a mountain number if the first three digits increase and the last three digits decrease. For example, 35763 is a mountain number but 35663 is not. How many five-digit numbers greater than 70000 are mountain numbers?
78910 , 78920 , 78921 , 78930 , 78931 , 78932 , 78940 , 78941 , 78942 , 78943 , 78950 , 78951 , 78952 , 78953 , 78954 , 78960 , 78961 , 78962 , 78963 , 78964 , 78965 , 78970 , 78971 , 78972 , 78973 , 78974 , 78975 , 78976 , 78980 , 78981 , 78982 , 78983 , 78984 , 78985 , 78986 , 78987 , Total = 36 such numbers
