Some digits are missing from this credit card number. If the sum of any three consecutive digits is 20, what is the value of x?

_ _ _5 - _ _ _ _- x_ _ _ - _8_ _

If you consider the sequence as: a, b, c, 5, d, e, f, g, x, h, i, j, k, 8 You then set up equations like: a+b+c = 20 ...(1) b+c+5 = 20 .... (2) c+5+d = 20 5+d+e=20 d+e+f=20 e+f+g=20 f+g+x=20 g+x+h=20 x+h+i=20 h+i+j=20 i+j+k=20 j+k+8=20 You then find solutions like: from eq(2)b+c+5 = 20or, b+c = 20-5 =15put this in eq (1),a+15 =20you get, a=5 similarly, you can find, b=d c=e f=5 g=b x=c h=5 i=b j=c k=5 b=8 If a = 5 and b = 8, then c = 7. Since x = c, x = 7. Please best my answer and add me as your tutor for further help. Thanks :)

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