<u>Answer: </u>
Option (c)
The average speed between 2.8 km and 4.2 km is 42 km/h
<u>Explanation:</u>
Given, the distance between 2.8 km and 4.2 km is 4.2 - 2.8 = 1.4 km
Time (in hours) between 2.8 km and 4.2 km
= 0.084 – 0.051
= 0.033 hr
Speed =
Speed = 
Speed = 42.4 km/hr = 42 km/h (rounded to nearest)
Therefore, the average speed between 2.8 km and 4.2 km is 42 km/hr
Hence, Option (C) is correct
The formula for a rectangle's perimeter is
P = 2l + 2w
We know the length is 2 ft greater than thrice the width, so 2l becomes:
3w + 2ft + 3w + 2ft
Substitute.
P = 3w + 2ft + 3w + 2ft + 2w
Add like terms.
P = 8w + 4ft
Substitute P.
84 ft = 8w + 4ft
Subtract 4 ft from both sides to eliminate. (Property of equality)
84 ft - 4ft = 8w + 4ft - 4ft
80 ft = 8w
Divide 8 on both sides to isolate w.
80 ft / 8 = 8w / 8
10 ft = w
We have the value of w, now look for the l which we know is 2 feet more than thrice the value of w.
l = 10 ft × 3 + 2 ft
l = 30 ft + 2 ft
l = 32 ft
Therefore, the length and the width of the rectangle is 10 ft (w) and 32 ft (l).
Check:
84 ft = (2) (10 ft) + (2) (32 ft)
84 ft = 20 ft + 64 ft
84 ft = 84 ft ✔
♧
John is correct. The substitution property is being used. The x is being substituted for the value 9 (aka x is replaced with 9). Keep in mind that x is simply a placeholder for a number, in this case 9.
Think of "substitution" as in a sports game where one player replaces another. Or you can think of a substitute teacher where someone else temporarily replaces your teacher for the day. Those are two ways to help remember the term.
The distributive property is not being used here since it is a*(b+c) = a*b+a*c. For example, 2*(3+5) = 2*3+2*5
