Join 60,000+ competitive exam aspirants
The first and last terms of an A.P. are 36 and 46. If the sum of its terms is 574, then the number of terms will be?
17
14
15
16
14
Use the average value property: Sum = (Average of first and last) * n. Here, (36+46)/2 = 41. Thus, 574 / 41 = 14.
First term a = 36, Last term l = 46, Sum of terms S = 574.
S=2nтАЛ(a+l)
Use the average value property: Sum = (Average of first and last) * n. Here, (36+46)/2 = 41. Thus, 574 / 41 = 14.
Students often confuse the sum formula with the general term formula anтАЛ=a+(nтИТ1)d and get stuck trying to find the common difference d, which is unnecessary.
Identify given parameters
We are provided with the first term a=36, the last term l=46, and the total sum S=574.
a=36,l=46,S=574
Set up the sum formula
The sum of an Arithmetic Progression given the first and last terms is given by the formula S=2nтАЛ(a+l).
574=2nтАЛ(36+46)
Calculate the number of terms
Simplify the sum of the terms inside the parentheses: 36+46=82. Then, 574=2nтАЛ├Ч82, which simplifies to 574=n├Ч41. Solving for n gives n=41574тАЛ=14.
n=14
Option B is correct because the calculation 574/41 yields exactly 14 terms.
The formula S=2nтАЛ(a+l) is a specific case of the general sum formula and is highly useful in time-saving during competitive exams for sequences and series.