Final answer:
The missing number in the equation 1,803 = 1,000 + 800 + ? is 3, found by subtracting the sum of 1,000 and 800 from 1,803.
Step-by-step explanation:
The student is asking for the missing number in the equation 1,803 = 1,000 + 800 + ? To find this number, we need to subtract the sum of 1,000 and 800 from 1,803.
1,803 - 1,000 - 800 = 3
Therefore, the missing number in the equation is 3.