Question 1
The third term of an Arithmetic Progression (A.P.) is 23 and the sum of the first seven terms is 210. Find the:
- Common difference;
- First term;
- Sum of the first 20 terms.
Observation
The Chief Examiner reported that a good number of candidates were able to interpret and solve correctly.
In part (a), they were expected to first express the third term as …..(1). Substitute 210 into sum of terms formula gives . Simplifying gives
…(2).Solving equation (1) and (2) gives .
In part (b), they were expected substitute into equation(1) to give . Simplifying gives . Solving gives .
In part (c), they were expected to substitute , into the sum of terms formula to give
Simplifying gives 10 = 1,510.