Question 1131195
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<pre>
There are 4 gaps between the first term and the fifth term of an AP.


So, each gap is  {{{(56-12)/4}}} = {{{44/4}}} = 11 units long.


Thus the common difference of the AP is 11.


The numbers that she can not see are


    {{{a[2]}}} = 12 + 11 = 23;

    {{{a[3]}}} = 23 + 11 = 34;

    {{{a[4]}}} = 34 + 11 = 45.
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Solved.