So we can start with the full of possibilities and eliminate them one by one.
The full set is {0,1,2,3,4,5,6,7,8,9}.
Now we know that any prime greater than 2 is odd as otherwise it would have 2 as a factor, so we can eliminate all of these digits that would be an even number, leaving:
{1,3,5,7,9}
We also know that any prime greater than 5 cannot be a multiple of 5 and that all numbers with 5 in the digits are a multiple of 5, so we can eliminate 5.
{1,3,7,9}
We know that 11,13,17 and 19 are all primes, so we cannot eliminate any more of these, leaving the set:
{1,3,7,9} as our answer.
Answer:
One number is 15 and 3 less than that is 12 so that is your other number
Add <span /><span><span><span><span><span><span>12</span></span><span /></span></span><span /></span><span>12</span></span> to both sides
<span /><span><span><span><span><span><span>8</span><span>x</span><span>=</span><span>5</span><span>x</span><span>+</span><span>15</span><span>+</span><span>12</span></span><span /></span></span><span /></span><span>8x=5x+15+12</span></span>
2<span> </span>Simplify <span /><span><span><span><span><span><span>5</span><span>x</span><span>+</span><span>15</span><span>+</span><span>12</span></span><span /></span></span><span /></span><span>5x+15+12</span></span> to <span /><span><span><span><span><span><span>5</span><span>x</span><span>+</span><span>27</span></span><span /></span></span><span /></span><span>5x+27</span></span>
<span /><span><span><span><span><span><span>8</span><span>x</span><span>=</span><span>5</span><span>x</span><span>+</span><span>27</span></span><span /></span></span><span /></span><span>8x=5x+27</span></span>
3<span> </span>Subtract <span /><span><span><span><span><span><span>5</span><span>x</span></span><span /></span></span><span /></span><span>5x</span></span> from both sides
<span /><span><span><span><span><span><span>8</span><span>x</span><span>−</span><span>5</span><span>x</span><span>=</span><span>27</span></span><span /></span></span><span /></span><span>8x−5x=27</span></span>
4<span> </span>Simplify <span /><span><span><span><span><span><span>8</span><span>x</span><span>−</span><span>5</span><span>x</span></span><span /></span></span><span /></span><span>8x−5x</span></span> to <span /><span><span><span><span><span><span>3</span><span>x</span></span><span /></span></span><span /></span><span>3x</span></span>
<span /><span><span><span><span><span><span>3</span><span>x</span><span>=</span><span>27</span></span><span /></span></span><span /></span><span>3x=27</span></span>
5<span> </span>Divide both sides by <span /><span><span><span><span><span><span>3</span></span><span /></span></span><span /></span><span>3</span></span>
<span /><span><span><span><span><span><span>x</span><span>=</span><span><span><span><span>27</span><span /></span><span><span>3</span><span /></span><span><span /><span /></span></span></span></span><span /></span></span><span /></span><span>x=273</span></span>
6<span> </span>Simplify <span /><span><span><span><span><span><span><span><span><span>27</span><span /></span><span><span>3</span><span /></span><span><span /><span /></span></span></span></span><span /></span></span><span /></span><span>273</span></span> to <span /><span><span><span><span><span><span>9</span></span><span /></span></span><span /></span><span>9</span></span>
<span /><span><span><span><span><span><span>x</span><span>=</span><span>9</span></span><span /></span></span><span /></span><span>x=9
</span></span>
The formula for finding the area of a cone is pi times the radius squared times the height/3. Since we already have the base area, all we need to do is find the height over 3. The height is 6, so 6/3=2. Then 4 pi times 2=8 pi.
The answer is 8pi.
