The expression for this problem can be shown as:
1/2n + 20 = 70
where n represents the number. We can solve by isolating the variable. To do this, we subtract 20 on both sides to make the equation become:
1/2n = 50
Let’s divide both sides by 1/2 to find that:
n = 100
We can substitute 100 into the initial equation for verification:
1/2(100) + 20 = 70
50 + 20 = 70
Since this is true, we now know that the number is 100.