Question

in a rangoli design of 13 rows every row increases its previus row by two dots and first row contains 5 dots then how many total dots are in the design

Answer 1

221

Step-by-step explanation:

series= 5,7,9..,

a= 5

d=2

so,S13= 13/2(2*5+12*2)

=13/2(10+24)

=13/2 *34

=13*17

S13 =221

Answer 2

Answer:

221

Step-by-step explanation:

required AP = 5, 5+2, 5+2(2), 5+3(2),...........[13th term}

first term of AP (a) = 5

Common difference (d) = 2

sum of first 13 terms of AP  =  S13

                                             =  n/2[2a+(n-1)d]

                                             =  13/2[2(5)+(13-1)(2)]                                                                

                                             =  13/2[10+24]

                                             =  13/2[34]

                                             =  13[17]

                                             =  221