Question

Look at the picture as I can’t type the whole thing

Answer 1

23.1 hours

Explanation:

the mean is calculated as

mean = ∑ fx ÷ ∑ f

where x is the midpoint of the time intervals

0 < h ≤ 10 ⇒ x = 5

10 < h ≤ 20 ⇒ x = 15

20 < h ≤ 30 ⇒ x = 25

30 < h ≤ 40 ⇒ x = 35

then

∑ fx = (5 × 5) + (15 × 15) + (50 × 25) + (10 × 35)

= 25 + 225 + 1250 + 350

= 1850

∑ f = 5 + 15 + 50 + 10 = 80

then

mean = 1850 ÷ 80 ≈ 23.1 hours (to 1 dp )