A) The first step needs 100 bricks, the second needs 98, the third needs 96, and so on. Therefore the number of bricks for the nth step is: a_n = a_1 + d(n-1), where a_1 = 100 (the first term), d = -2 (difference).
a_n = 100 - 2(n-1) = 102 - 2n, and for the 30th step, a_30 = 102 - 2*30 = 42. So the top step will need 42 bricks.
b) The total staircase will need: 100 + 98 + 96 + ... + 44 + 42, and there are n = 30 terms. Using the formula for the sum of an arithmetic sequence:
S = (a_1 + a_n)*n/2 = (100 + 42)*30/2 = 2130
Therefore, 2130 bricks are required to build the entire staircase.
Answer:
(-1, 3)
Step-by-step explanation:
x - 5y = -16 [Equation 1]
-x + 3y = 10 [Equation 2]
<u>Adding both equations</u>
- x - x - 5y + 3y = -16 + 10
- -2y = -6
- y = 3
- x - 5(3) = -16
- x - 15 = -16
- x = -1
<u>Solution</u> : (-1, 3)
The answer is B) 6xy and -16xy
Answer:
80 seconds
Step-by-step explanation:
