Answer:
DE = 20units
Step-by-step explanation:
In Δ ABC,
angle A is congruent to angle B.... (given)
therefore, ΔABC is an isoceles triangle.
therefore, CA = CB..... (side opposite to congruent angles are congruent in an isoceles triangle)
therefore, CB = 4 units
In ΔCDE,
angle D is congruent to angle E.... (given)
therefore, ΔCDE is an isoceles triangle.
therefore, CD = CE
therefore, CD = 8 units
ΔCDE ~ ΔCBA
therefore,

The average value over the interval is the area under the curve divided by the width of the interval.
Area = 4*(6 -1) +5(8 -6) = 30
Width = 8 - 1 = 7
Average value = 30/7 = 4 2/7
2/7 is the probability that the first satellite sends a weak signal. That leaves 6, one of which sends a weak signal. So the probability that the second also sends a weak signal is 1/6. Combine these and we get 2/7×1/6=1/21.