How many 3 digit palindromes are divisible by 9?

Mathematics

1 answer:

ludmilkaskok [199]3 years ago

3 0

Interesting problem.

A palindrome is a number which is identical when read/interpreted left-to-right or right-to-left. For example, 14241 is a palindrome, so is 444444.

A three digit palindrome must be made up of two distinct digits only, one for the first and last digits, and one for the middle, for example, 424, or 515, etc.

For a number to be divisible by 9, the sum of the digits must add up to a multiple of 9, such as 0, 9, 18, 27, etc.

We can now form a table of the possible 3-digit palindromes divisible by 9, starting with the first/last digits (=A), and finding the middle digit (=B). The number is therefore represented by the pattern ABA.

For example, when A=1, we have the number 1B1. For the number to be divisible by 9, B=7 so that sum=1+7+1=9, which is divisible by 9.

For each value of A (from 1 to 9) we can only find one value of B that makes the number divisible by 9. Thus we can only find nine such numbers, with A equal to 1 to 9.

Here's a list of the numbers

A B number

1 7 171

2 5 252

3 3 333

4 1 414

5 8 585

6 6 666

7 4 747

8 2 828

9 0 909

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Oduvanchick [21]

Given the table below representing the number of hours of television nine Math II class students watched the night before a big test on triangles along with the grades they each earned on that test.

$\begin{center}
\begin{tabular}
{|c|c|}
Hours Spent Watching TV & Grade on Test (out of 100) \\ [1ex]
4 & 71 \\ 
2 & 81 \\ 
4 & 62 \\ 
1 & 86 \\ 
3 & 77 \\ 
1 & 93 \\ 
2 & 84 \\ 
3 & 80 \\ 
2 & 85
\end{tabular}
\end{center}$

Let the number the number of hours of television each of the students watched the night before the test be x while the grades they each earned on that test be y.

We use the following table to find the equation of the line of best fit of the regression analysis of the data.

$\begin{center} \begin{tabular} {|c|c|c|c|} x & y & x^2 & xy \\ [1ex] 4 & 71 & 16 & 284 \\ 2 & 81 & 4 & 162 \\ 4 & 62 & 16 & 248 \\ 1 & 86 & 1 & 86 \\ 3 & 77 & 9 & 231 \\ 1 & 93 & 1 & 93 \\ 2 & 84 & 4 & 168 \\ 3 & 80 & 9 & 240 \\ 2 & 85 & 4 & 170 \\ [1ex]\Sigma x=22 & \Sigma y=719 & \Sigma x^2=64 & \Sigma xy=1,682 \end{tabular} \end{center}$

Recall that the equation of the line of best fit of a regression analysis is given by
$y=a+bx$
where:
$a= \frac{(\Sigma y)(\Sigma x^2)-(\Sigma x)(\Sigma xy)}{n(\Sigma x^2)-(\Sigma x)^2}$
and
$b= \frac{n(\Sigma xy)-(\Sigma x)(\Sigma y)}{n(\Sigma x^2)-(\Sigma x)^2}$

$y=\frac{(719)(64)-(22)(1,682)}{9(64)-(22)^2}+\frac{9(1,682)-(22)(719)}{9(64)-(22)^2}x \\ \\ = \frac{46,016-37,004}{576-484} + \frac{15,138-15,818}{576-484} x \\ \\ = \frac{9,012}{92} + \frac{-680}{92} x \\ \\ =97.95-7.391x$

Thus, the equation of the line of best fit is given by y = 97.95 - 7.391x

<span>A student that watched 1.5 hours of TV will have a score given by
y = 97.95 - 7.391(1.5) = 97.95 - 11.0865 = 86.8635

Therefore, </span><span>a student’s score if he/she watched 1.5 hours of TV to the nearest whole number is 87.</span>

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