The following bar graph shows the circulation growth of a magazine ABC from July 2022 to December 2022. July — 173182 August — 175395 September — 189277 October — 200189 November — 204933 December — 211885 During October to December there was an even growth rate, the average of which, is (correct up to one decimal place):

Correct — D. Take the two month-on-month growths that lie inside the October-to-December window and average them.

Bar values: Oct = 200189, Nov = 204933, Dec = 211885

Oct → Nov: 4744⁄200189 × 100 = 2.37%
Nov → Dec: 6952⁄204933 × 100 = 3.39%

Average = (2.37 + 3.39)⁄2 = 2.88% ≈ 2.9% → option (d)

Why the others are wrong

• (a)
  3.2% — 3.2% is not the midpoint of the two monthly rates. Those rates are 2.37% and 3.39%, and the mean of any two numbers sits centrally between them — here at 2.88%.
• (b)
  2.4% — 2.4% is the October → November growth on its own, 2.37% rounded. The November → December rise of 3.39% still has to be averaged in.
• (c)
  3.8% — 3.8% is the average once September is wrongly dragged in. September → October is 5.77%, and (5.77 + 2.37 + 3.39)⁄3 = 3.84%. The window starts at October.

A growth rate is measured against the earlier value, never the later one.

October → November uses 200189 as the base and November → December uses 204933. Shifting the base is what produces the near-miss answers in bar-graph DI.

'October to December' names two intervals, not three. October's own rise belongs to the September → October step and sits outside the window.

Key facts

• The bar labels read October 200189, November 204933 and December 211885.
• Growth rate = (rise ÷ earlier value) × 100, so the base changes every month.
• October → November is 2.37% and November → December is 3.39%.

Common traps

• Using the later month as the base, which gives 2.31% and 3.28%.
• Counting three growth steps in a window that contains only two.
• Averaging the circulation figures instead of the growth rates.

No directly related past PYQ was found.