So i got 90 4/7 reduced in fractions
Let's start by visualising this concept.
Number of grains on square:
1 2 4 8 16 ...
We can see that it starts to form a geometric sequence, with the common ratio being 2.
For the first question, we simply want the fifteenth term, so we just use the nth term geometric form:


Thus, there are 16, 384 grains on the fifteenth square.
The second question begs the same process, only this time, it's a summation. Using our sum to n terms of geometric sequence, we get:



Thus, there are 32, 767 total grains on the first 15 squares, and you should be able to work the rest from here.
<h3>
Answer: -19, -15, -9, -1, 9 (choice A)</h3>
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Explanation:
If we plug in x = -2, then we get,
y = x^2 + 7x - 9
y = (-2)^2 + 7(-2) - 9
y = 4 - 14 - 9
y = -10 - 9
y = -19
So x = -2 leads to y = -19. The answer is between A and D.
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If you repeat those steps for x = -1, then you should get y = -15
Then x = 0 leads to y = -9
x = 1 leads to y = -1
Finally, x = 2 leads to y = 9
The outputs we get are: -19, -15, -9, -1, 9 which is choice A
Choice D is fairly close, but we won't have a second copy of -15, and we don't have an output of -19.
Answer:



This might not be correct though. I'm only in middle school lol. I am sure about the last one.