Question 853270
Necklace Row I -------- 3

Row II------------------10

Row III-----------------17

common difference between rows is 7. d=7
The first row has 3 so a= 3
Number of rows = 18

It is an Arithmatic Progression

The summation {{{ Sn = (n/2)( 2a + (n-1)d)}}}


{{{Sn = (18/2)(2*3 + (18-1) * 7)}}}

= 9(6+17*7)

= 9(6+119)

=9*125

= 1125

The total beads = 1125