Order of operations

The expression 3 + 4 * 5 is a short way of describing a real situation. Picture 4 bags of 5 apples plus 3 loose apples. You would count the 4 * 5 apples inside the bags first, then add the 3 loose ones. That is why multiplication gets done first: it describes one grouped amount, while addition shows separate amounts lying side by side.

Jordan went left to right, adding 3 + 4 = 7 first. That changed the meaning: he computed (3 + 4) * 5 = 35, which is 7 groups of 5. Left to right is only the rule when the operations have equal rank, like 6 - 2 + 4, where going left to right gives the agreed answer. With mixed ranks, left to right stops being safe.

The fix begins inside the expression: find the multiplication and do it first. 4 * 5 = 20, so the expression shrinks to 3 + 20. Then the addition is the only move left, and 3 + 20 = 23. One operation at a time, and the long expression shortens step by step into the answer. Cross off each computed part as you go, and nothing gets reused twice.

Check by reading 3 + 20 as a situation: 3 apples and 20 apples is 23 apples. The written conventions exist so that anyone reading the expression computes the same value, and multiplying before adding is the order everyone agrees on. If the words for 3 + 4 * 5 were instead (3 + 4) * 5, parentheses would say so.