There are four people A, B, C, and D. It is known that the average age of A, B, and C is 1 year older than the average age of the four people, and the average age of A, B, and C is older than the average age of A, B, and C. One year older, A is 4 years older than B, and D is 17 years old, so how old is A?
有甲、乙、丙、丁四个人，已知甲、乙、丙三人的平均年龄比四人的平均年龄大1岁，甲、乙的平均年龄比甲、乙、丙三人的平均年龄大1岁，甲比乙大4岁，丁17岁，那么甲多少岁．
<gadget id="calculator">17 / 4</gadget>
<output>17/4 = around 4.25</output>

<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">5 / 4</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(17/4) - 1 - (5/4)</gadget>
<output>2</output>

<gadget id="calculator">3 + 1 + 2</gadget>
<output>6</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4) - (1/4) - (1/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">6 / (1/4)</gadget>
<output>24</output>

<result>24</result>