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Grade: 12

                        

Given an A.P. whose terms are all positive integers. The sum of its first nine terms is greater then 200 and less than 220. If the second term in it is 12, then its 4th term is. :

6 years ago

Answers : (3)

Sher Mohammad
IIT Delhi
askIITians Faculty
174 Points
							a+d=12
sum of first 9 terms 200<a+8d<220
200-12<a+8d-a-d<220-12
188<7d<208
27<d <29
taking d=28, 4th term is a+3d=-16+3*28 ,

sher mohammad
b.tech, iit delhi





6 years ago
sai krishna
20 Points
							sum of n terms in an A.P = N/2[2a+(n-1)d]
So, sum to 9 terms= 9/2[2a+8d]
According to given question, 200<9/2[2a+8d]<220
                                              =  200<9[a+4d]<220
                                              = 200/9
                                    
6 years ago
sai krishna
20 Points
							sum of n terms in an A.P = N/2[2a+(n-1)d]
So, sum to 9 terms= 9/2[2a+8d]
According to given question, 200<9/2[2a+8d]<220
                                              =  200<9[a+4d]<220
                                              = 200/9
                                    
6 years ago
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