Question 953373
<pre>
{{{matrix(1,3,A,""="",h((a+b)/2))}}} 

We are told that h=4 cm and A=20 cm square

{{{matrix(1,3,20,""="",4((a+b)/2))}}}

Simplify by dividing the 2 into the 4:

{{{matrix(1,3,40,""="",2(a+b))}}}

Divide both sides by 2

{{{matrix(1,3,20,""="",a+b)}}}

{{{matrix(1,3,a+b,""="",20)}}}

Since a is smaller than b and their sum is 20,
we can have any of these where a and b are whole numbers.

a = 1, b = 19, a < b and a + b = 1 + 19 = 20
a = 2, b = 18, a < b and a + b = 2 + 18 = 20
a = 3, b = 17, a < b and a + b = 3 + 17 = 20
a = 4, b = 16, a < b and a + b = 4 + 16 = 20
a = 5, b = 15, a < b and a + b = 5 + 15 = 20
a = 6, b = 14, a < b and a + b = 6 + 14 = 20
a = 7, b = 13, a < b and a + b = 7 + 13 = 20
a = 8, b = 12, a < b and a + b = 8 + 12 = 20
a = 9, b = 11, a < b and a + b = 9 + 11 = 20




Edwin</pre>