12. If the sum of all 21 terms of an arithmetic progression is zero, then which of the following MUST be true ? (An arithmetic progression is a sequence of numbers such that the difference between the consecutive terms is constant)
I. 11th smallest term is zero
II. 11th largest term is zero
III. The range of the numbers is 20A. I
B. II
C. III
D. I and II
E. None of the above
Solution:This is a MUST BE TRUE question so any statement if true, MUST BE TRUE under any and all circumstances
Given: An Arithmetic Progression of 21 terms & Sum of AP = 0
Analysis: For sum of all terms of AP to be 0, there can be two cases
a) Half the terms are Negative, Half are Positive and the middle term = 0
b) All terms = 0 (AP with Common Difference = 0)I. 11th smallest term is zero
In either of the 2 above cases, 11th smallest term will always be 0. MUST BE TRUE
II. 11th largest term is zero
In either of the 2 above cases, 11th largest term will always be 0 (21 terms AP, 11th smallest term = 11th largest term). MUST BE TRUE
III. The range of the numbers is 20
No, the range depends on the first and last terms of the AP
Range of consecutive integers from -10 to + 10 = 20
Range of consecutive even integers from -20 to +20 = 40
NOT MUST BE TRUE
So, I & II are ALWAYS TRUE
Answer: D