# CBSE Class 10-Mathematics: Chapter –3 Pair of Linear Equation in Two Variables Part 20

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**Question 20:**

A says to B my present age is five times your that age when I was an old as you are now. It the sum of their present ages is 48 years, find their present ages.

**Answer:**

Let the present age of years

And years

According to question,

**Question 21:**

A boat goes upstream and downstream in hours. In hours it can go upstream and down stream. Determine the speed of the stream and that of the boat in still water.

**Answer:**

Let the speed of boat is in still water

And stream

According to question,

And

Let

On solving eq. (i) and (ii) we get,

On solving eq. (iii) and (iv) we get,

**Question 22:**

Determine graphically the coordinates of the vertices of the triangle, the equation of whose sides are and .

**Answer:**

When

When

When

**Question 23:**

Father’s age is three times the sum of ages of his two children. After years, his age will be twice the sum of ages of two children. Find the age of father.

**Answer:**

Let the present age of father be years and sum of present age of two son’s be year’s

According to question,

After five years

And

Or