Question

to add number to sum, you write ______. (note: java is case-sensitive.)
a number += sum;
b sum = sum + number;
c number = sum + number;
d sum += number;
e sum = number + sum;

Explanation:

• Option A: number += sum; adds sum to number, not what we want (we need to add number to sum).
• Option B: sum = sum + number; correctly adds number to the current value of sum and stores the result back in sum.
• Option C: number = sum + number; updates number by adding sum to it, not sum.
• Option D: sum += number; is a shorthand for sum = sum + number;, so it also correctly adds number to sum.
• Option E: sum = Number + sum; uses Number (with a capital 'N') which is different from number (case - sensitive in Java), so it will cause an error if Number is not defined, and it's not the correct variable name as per the problem's context.

Both B and D are correct as they achieve the goal of adding number to sum. But if we consider the common shorthand notation, D is also very common. However, let's analyze the intention:

The task is to add number to sum. Let's check each option:

• A: Modifies number by adding sum to it. Incorrect.
• B: sum is updated to its current value plus number. Correct.
• C: Modifies number by adding sum to it. Incorrect.
• D: Shorthand for sum = sum + number, so it also adds number to sum. Correct.
• E: Uses Number (wrong case) and modifies sum with an undefined (probably) variable. Incorrect.

If we have to choose the most appropriate, both B and D are correct. But let's see the options again. The question says "to add number to sum", so the target variable is sum. So both B (sum = sum + number;) and D (sum += number;) are correct.

Answer:

B. sum = sum + number;
D. sum += number;