1.   A man’s age is four times that of his son in 20 years he will be only twice as old as his son. Find his present age.

Let's denote the man's current age as \( M \) and his son's current age as \( S \).

According to the problem, we have two pieces of information:

1. The man's age is four times that of his son:
\[ M = 4S \]

2. In 20 years, the man will be twice as old as his son:
\[ M + 20 = 2(S + 20) \]

We can solve these equations step-by-step.

First, substitute the first equation into the second equation:
\[ 4S + 20 = 2(S + 20) \]

Now, expand and simplify:
\[ 4S + 20 = 2S + 40 \]

Subtract \( 2S \) from both sides:
\[ 2S + 20 = 40 \]

Subtract 20 from both sides:
\[ 2S = 20 \]

Divide both sides by 2:
\[ S = 10 \]

Now that we have the son's age, substitute \( S = 10 \) back into the first equation to find the man's age:
\[ M = 4S \]
\[ M = 4 \times 10 \]
\[ M = 40 \]

So, the man's current age is \( 40 \) years old.

Would you like any more details or have any questions about this solution? Here are five more questions you might find interesting:

1. How can you find the roots of a quadratic equation?
2. What is the derivative of \( x^3 + 3x^2 - 4x + 7 \)?
3. How do you solve a system of linear equations using the matrix method?
4. What is the integral of \( \sin(x) \cos(x) \)?
5. How do you calculate the area of a triangle given its three vertices?

**Tip:** When solving word problems, it's helpful to clearly define variables and write down all given relationships as equations.

Learn how to solve a word problem involving a man's age being four times his son's age and how this relationship evolves over time. Includes step-by-step solution and clear explanation of algebraic concepts. Suitable for students in Grades 7-9.

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