IB Math AA HL Paper 3 - Finding EASY marks!

Summary

The video demonstrates how to find marks in IB Mathematics AA HL Paper 3 even when earlier parts of a question are difficult. Paper 3 contains two multi-part questions worth 55 marks in total, so the presenter recommends managing time strategically and looking for later parts that can be answered independently.

Using Question 1 from the May 2024, Time Zone 1 paper, the presenter highlights several opportunities:

Follow explicit instructions

In part C(i), the question asks students to differentiate the given infinite geometric-series equation with respect to (R). Differentiating term by term and applying the chain rule to the closed-form expression gives

[ A + 2AR + 3AR^2 + \cdots = \frac{A}{(1-R)^2}. ]

This part can be attempted even without understanding the earlier parts of the question.

Use results supplied in the question

Part D provides expressions for (E(X)) and (\operatorname{Var}(X)). Substitute (P=0.1) into each expression, using a calculator if needed. The presenter identifies this as a straightforward opportunity to earn marks, even if part C(ii) is unresolved.

Look for simple reasoning in later parts

In the second model, the boost probability increases by (0.2) with each action. By the fifth action, the probability of a boost is (1), so a boost must have occurred by then. Therefore, the number of actions until the boost is at most five.

Use the probability table or tree structure

• To find (M), the probability that the first boost occurs on the second action, multiply the probability of no boost on the first action by the probability of a boost on the second: [ 0.8 \times 0.2. ]

• Find (N) by continuing the probability-tree reasoning or by using the fact that all probabilities in the table must add to (1).

Apply standard discrete-random-variable calculations

• Find (E(Y)) by multiplying each possible value of (Y) by its probability and adding the results.
• Use the provided variance formula to find (\operatorname{Var}(Y)).

Broader lesson

Keep scanning a question for self-contained tasks, such as direct substitution, basic probability reasoning, or a clearly specified procedure. Getting stuck on one part does not mean the rest of the question is inaccessible. The presenter estimates that several marks—including roughly six in one later section—may be available without solving the entire problem.

Speakers and sources

• Speaker: One presenter from the IB Maths Dr. channel; no other speakers are featured.
• Source discussed: Question 1 of the May 2024 IB Mathematics AA HL Paper 3, Time Zone 1.