help me for past one week none asnwered?

Question

Constructing a Brick Staircase : A brick staircase has a total of 30 steps . The bottom steps requires 100 bricks . Each successive step requires two less bricks than the prior step.
(a) How many bricks are required for the step top step ?
(b) How many bricks are required to build the staircase ?

i am confused which one is the right ?

Answer 1

So 100+98+96+94+92+90+88+86, etc. until you have 30 numbers to add up. The last number out of the 30 is your number of bricks for the top step. The total added together is the number for the entire staircase.
Maybe no one answered because this is real simple and they thought you would figure this out for yourself.

Answer 2

(A) Each subsequent step is 2 less than the previous, so the 30th step is (30-1)*2 less than the 1st.

The top step requires 100 - 58 = 42 bricks.

(Don't forget that the 30th step is only 29 steps AFTER the 1st step! It is a common error to assume that the 30th step would be 100-(2*30) = 40 bricks, but this is wrong.)

(B) You need to find the sum of 100 + 98 + 96 + 94 + ... + 42

The sum of a linear sequence is the sum of the first and last terms, times the number of terms in the sequence, divided by two:

(100 + 42) * 30 / 2

= 2,130

(Alternatively, that's also the average of the first and last term, times the number of terms.)

The 30,000 answer which someone below suggested is clearly incorrect -- that's 1,000 bricks per each of the 30 steps which cannot be right.

Answer 3

30th step = 100 bricks 29th = 98 bricks 28th = 96 bricks
27th step = 94 bricks 26th = 92 bricks 25th = 90 bricks, etc... 1st step=42 bricks

answer (a). is 42 bricks

100+98+96+94+92+90+ etc.= 2050

answer (b). is 2050

Answer 4

a)

100-2*30= 40 bricks

b)

40+42+44.....96+98+100= 31500 Bricks