CA Foundation · Quantitative Aptitude · Measures of Central Tendency and Dispersion
The monthly electricity bills (in ₹) of nine households in a Jaipur colony, arranged in ascending order, are 420, 480, 510, 560, 600, 650, 720, 800, 950. What is the value of the first quartile Q1, using the (n+1)/4 th item rule?
The first quartile is ₹495. With nine observations, Q1 is the 2.5th item, which lies midway between the second value, 480, and the third value, 510. Their average gives 495, so the value is not an actual observation in the list.
- A480
- B495Correct
- C510
- D560
Explanation
n = 9, so Q1 is the (9+1)/4 = 2.5th item. This lies halfway between the 2nd item (480) and the 3rd item (510), so Q1 = (480+510)/2 = 495. Choosing 480 wrongly takes the 2nd item instead of the 2.5th.
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