A cricket is an insect - HSC - SSCE Mathematics Advanced - Question 27 - 2020 - Paper 1

Since a total of 684 chirps were counted over 20 days, we find the mean number of chirps:

$ȳ = \frac{684}{20} = 34.2$

Substituting x̄ and ȳ into the regression equation:

$34.2 = -10.6063 + b(21.475)$

To find b, rearranging gives us:

$b = \frac{34.2 + 10.6063}{21.475} = 2.08644$

Now, we substitute x = 19 into the regression equation:

$y = -10.6063 + 2.08644 \times 19$
Calculating this:

$y = -10.6063 + 39.64436 = 29.0381$

Rounding to the nearest whole number gives:

29 chirps