Question

1) The sum of the two numbers is 36 and their difference is 9. Find the average of the two numbers.

Answer 1

Let the two numbers be x and y

x+y = 36 -----(1)

x - y = = 9-----(2)

(1)+(2)

x +y = 36

x - y = 9

---------------

2x = 45

x = 45/2

Then y =?

x - y =9

45/2 - y =9

y = 45/2-9

y = (45-18)/2

y = 27/2

The two numbers are 45/2 and 27/2

Answer 2

22.5 and 13.5 are the numbers. average of both numbers is 18.

Explanation:

Given that there are two numbers.

let them be, x and y

using the unknown numbers,

• x + y = 36
• x - y = 9

make x the subject:

• x + y = 36
• x = 36 - y ..........equation 1

• x - y = 9
• x = 9 + y ..........equation 2

Solve them simultaneously:

• 9 + y = 36 - y
• y + y = 36 - 9
• 2y = 27
• y = 13.5

Then another number, x:

• x = 9 + y
• x = 9 + 13.5
• x =22.5

Average:

• ( sum of both the numbers ) ÷ 2
• ( 22.5 + 13.5 ) ÷ 2
• 18