Flag Discuss with Askiitians Tutors> A.P. Questions...
question mark

1. Find the sum of the 1st 25 terms on A.P. whose nth term is given by tn=2-3n.2. Find the sum of all two digits natural numbers which when divided by 3 yield 1 as remainder.3. A man borrows Rs. 1000 and agrees to repay with a total interest of Rs. 140 in 12 installments. Each instalment being less than the preceding by Rs. 10. What should be his 1st instalment?

Kurma Anudeep , 13 Years ago
Grade 10
anser 3 Answers
Devesh Lall

Last Activity: 13 Years ago

SOLUTION FOR QUESTION NO.-1 --------  tn=2-3n (given)

1st term=t1=2-3x1

                =-1

sly.

2nd term=t2=2-3x2

                 =-4

now, d(common difference)=t2-t1=-4-(-1)=-3 

since n=25

therefore, sum of 1st 25 terms=sn=n/2[2a+(n-1)d]

                                                =25/2[2x-1+(25-1)-3]

                                                =-925

Devesh Lall

Last Activity: 13 Years ago

SOLUTION FOR QUESTION NO.-2 ---------

since 2-digits no.s starts from 10 & ends at 99

therefore required no.s which when divided by 3 leaves remainder 1 are:- 10,13,16,19,................,94,97

here the 1st term(a) is 10 & c.d.(d) is 3 & the last term is 97(l).

now,

l=a+(n-1)d

97=10+(n-1)3

n=30

sn=n/2[2a+(n-1)d] (sum of the terms to nth term)

   =30/2[2x10+29x3]

   =1605

Devesh Lall

Last Activity: 13 Years ago

SOLUTION FOR QUESTION NO.-3

Since amt borrowed by a man earlier = Rs 1000

 "      total interst offerd to him in 12 installments = Rs 140

Now, let total overall amt be with the man be Sn =Rs (1000+140)

                                                                    = Rs 1140

"      "   his 1st installment be a 

"      " n be the no of installments = 12

"      " d " =-10

"  using the formula :-   Sn=n/2[2a+(n-1)d]

                                 1140=12/2[2a+11x-10]

                                 1140=6[2a-110]

                                 1140=12a-660

                                 12a=1140+660

                                 12a=1800

                                    a= Rs 150     

Therefore his required 1st installment = Rs 150

Provide a better Answer & Earn Cool Goodies

Enter text here...
star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments


Ask a Doubt

Get your questions answered by the expert for free

Enter text here...