Answer:
51 rows
Step-by-step explanation:
Given
Length of bookmark = 20cm
Distance between beads = 4mm
Required
Number of rows of beads
First, the distance between the rows of beads must be converted to cm
if 1mm = 0.1cm
then
4mm = 4*0.1cm
4mm = 0.4 cm
This means that each row of beads is placed at 0.4 cm mark.
The distance between each row follows an arithmetic progression and it can be solved as follows;
[tex]T_n = a + (n-1)d[/tex]
Where [tex]Tn = 20cm[/tex] (The last term)
[tex]a = 0 cm[/tex] (The first term)
[tex]d = 0.4cm[/tex] (The distance between each row of beads)
n = ?? (number of rows)
Solving for n; we have the following;
[tex]T_n = a + (n-1)d[/tex] becomes
[tex]20 = 0 + (n-1)0.4[/tex]
[tex]20 = (n-1)0.4[/tex]
DIvide both sides by 0.4
[tex]\frac{20}{0.4} = \frac{(n-1)0.4}{0.4}[/tex]
[tex]50 = (n-1)[/tex]
[tex]50 = n-1[/tex]
Add 1 to both sides
[tex]50 + 1= n-1 + 1[/tex]
[tex]n = 51[/tex]
Hence, the number of rows of beads is 51
