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Answer:
81 * 4 = 324.
Step-by-step explanation:
There are 81 * 4 = 324 such integers.
There are 9000 four-digit integers from 1000 to 9999. Let’s refer to the digit that occurs three times as the triplet and the digit that occurs once as the singleton.
In the first (most significant) position there are 9 possible values for the singleton, 1 through 9. In each case there are also 9 possible values for the triplet. For example if the singleton was a 1, the triplets could be anything but a 1: 1000, 1222, 1333, …, 1999. So there are 9 * 9 = 81 cases with the singleton in the first position.
A singleton in the second position can have 10 possible values, 0 through 9. If it’s a 0 there are 9 possible values for the triplet: 1011, 2022, 3033, …, 9099. If it’s anything else there are only 8 possible values for the triplet since the triplet cannot be 0: 2122, 3133, 4144, …, 9199. So there are 9 + (8 * 9) = 81 cases with the singleton in the second position.
The third and fourth positions work just like the second. So the grand total is 81 * 4 = 324.
If you plot the 9000 four-digit integers as a 100 x 90 grid of squares and color the integers with three same digits in red, an interesting pattern occurs:
There are 81 * 4 = 324 such integers.
There are 9000 four-digit integers from 1000 to 9999. Let’s refer to the digit that occurs three times as the triplet and the digit that occurs once as the singleton.
In the first (most significant) position there are 9 possible values for the singleton, 1 through 9. In each case there are also 9 possible values for the triplet. For example if the singleton was a 1, the triplets could be anything but a 1: 1000, 1222, 1333, …, 1999. So there are 9 * 9 = 81 cases with the singleton in the first position.
A singleton in the second position can have 10 possible values, 0 through 9. If it’s a 0 there are 9 possible values for the triplet: 1011, 2022, 3033, …, 9099. If it’s anything else there are only 8 possible values for the triplet since the triplet cannot be 0: 2122, 3133, 4144, …, 9199. So there are 9 + (8 * 9) = 81 cases with the singleton in the second position.
The third and fourth positions work just like the second. So the grand total is 81 * 4 = 324.
If you plot the 9000 four-digit integers as a 100 x 90 grid of squares and color the integers with three same digits in red, an interesting pattern occurs:
(If you zoom in, the four-digit number is printed inside each red square - not sure whether or not that will come through after Quora processes the image.)
Hope this helps!
Brain-List?
Answer: right side behavior:
f(x) is Decreasing
g(x) is Increasing
h(x) is Increasing
j(x) is Decreasing
<u>Step-by-step explanation:</u>
The rules for end behavior are based on 2 criteria: Sign of leading coefficient and Degree of polynomial
<u>Sign of leading coefficient</u> (term with greatest exponent):
- If sign is positive, then right side is increasing
- If sign is negative, then right side is decreasing
<u>Degree of polynomial</u> (greatest exponent of polynomial:
- If even, then end behavior is the same from the left and right
- If odd, then end behavior is opposite from the left and right
f(x) = -2x²
- Sign is negative so right side is decreasing
- Degree is even so left side is the same as the right side (decreasing)
as x → +∞, f(x) → +∞ Decreasing
as x → -∞, f(x) → -∞ Decreasing
g(x) = (x + 2)³
- Sign is positive so right side is increasing
- Degree is odd so left side is opposite of the right side (decreasing)
as x → +∞, f(x) → +∞ Increasing
as x → -∞, f(x) → -∞ Decreasing
- Sign is positive so right side is increasing
- Degree is an even <u>fraction</u> so left side is opposite of the right side as it approaches the y-intercept (-1)
as x → +∞, f(x) → +∞ Increasing
as x → -∞, f(x) → -1 Decreasing to -1
- Sign is negative so right side is decreasing
- Degree is odd so left side is opposite of the right side (increasing)
as x → +∞, f(x) → +∞ Decreasing
as x → -∞, f(x) → -∞ Increasing