Which number is irrational?

Irrational numbers are numbers that cannot be expressed as the ratio of two whole numbers. This is opposed to rational numbers, like 2, 7, one-fifth and -13/9, which can be, and are, expressed as the ratio of two whole numbers.

1. Callum = 2; Eilidh = 17; Caitlin's =22.

2. Ewan = 44; tree = 308.

Explanation:

Q1. Callum, Eilidh, and Caitlin

Let x = Callum's age

     y = Eilidh's age

     z = Caitlin's age

We have three conditions.

(1)  x = y - 5

(2) z = y + 15

(3) x + y + z = 31

Step 1. Eliminate one of the variables in two of the equations

Subtract (1) from (2):                      z - x = 20

Rearrange:                 (4)             -x + z = 20

Solve (2) for y:           (5)                     y = z - 15

Substitute into (3):         x +  z - 15  + z = 31

                                 (6) x + 2z             = 46

Step 2. Set up two new equations in two variables

(5)                          -x +   z = 20

(6)                           x + 2z = 46

Add (5) and (6):           3z = 66

Divide each side by 2: z = 22

Step 3. Substitute z into (5)

-x + 22 = 20

 x          = 2

Step 4. Substitute x into (1)

                                    2 = y - 5

Add 5 to each side     y = 7

Callum's age is 2; Eilidh's age is 7; Caitlin's age is 22.

Q2. Ewan and the tree

Let x = Ewan's age

      y = tree's age

We have two conditions.

                                     (1)          y = 7x

                                     (2)   x + y = 352

Rearrange (1)                (3) -7x + y =     0

                                     (2)    x + y = 352

Subtract (3) from (2)          8x       = 352

Divide each side by 8         x       =    44

Substitute y into (1)                    y = 7 × 44

                                                  y =   308

Ewan's age is 44; the tree's age is 308.