Let the present ages of A and B be $6x$ and $4x$ respectively, where $x$ is a constant multiplier for the ratio.

Step 1: Form equation based on the information

We know that 5 years ago, the ratio of their ages was 5:3. Therefore:

$\frac{6x - 5}{4x - 5} = \frac{5}{3}$

Step 2: Solve the equation

Cross-multiply to eliminate the fractions:

$3(6x - 5) = 5(4x - 5)$

Expanding both sides:

$18x - 15 = 20x - 25$

Step 3: Isolate $x$

Simplify and move the terms involving $x$ to one side:

$18x - 20x = -25 + 15$

$-2x = -10$

$x = 5$

Step 4: Calculate A's age

Since $x = 5$, the present age of A is:

$6x = 6 \times 5 = 30$

So, A is 30 years old.

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Do you want further details or have any questions?

Here are 5 related questions:

1. What is B's current age?
2. How old was A five years ago?
3. How will the ratio of their ages change in 10 years?
4. Can we find the total of their ages using the given information?
5. How would the solution change if the ratios were different?

Tip: When solving problems involving ratios and ages, always express ages in terms of a single variable for easier manipulation.