设甲数为a
乙数为b
甲乙两数的差是1902
a-b = 1902
a = b+1902
甲数除以乙数的商20,余数是21
(a-21)/b = 20
a = 20b + 21
b+1902 = 20b+21
19b = 1881
b = 99
a= 2001
甲数=2001
乙数=99