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Algebra Difficulty 2.5 Junior Find the answer

If wxyzwxyz is a four-digit positive integer with w0w \neq 0, the layer sum of this integer equals wxyz+xyz+yz+zwxyz + xyz + yz + z. If the layer sum of wxyzwxyz equals 2014, what is the value of w+x+y+zw + x + y + z?

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

The layer sum of wxyzwxyz equals 2014. This means that the sum of the integer with digits wxyzwxyz, the integer with digits xyzxyz, the integer with digits yzyz, and the integer zz is 2014. Note that the integer with digits wxyzwxyz equals 1000w+100x+10y+z1000w + 100x + 10y + z, the integer with digits xyzxyz equals 100x+10y+z100x + 10y + z, and the integer with digits yzyz equals 10y+z10y + z. Therefore, we have (1000w+100x+10y+z)+(100x+10y+z)+(10y+z)+z=2014(1000w + 100x + 10y + z) + (100x + 10y + z) + (10y + z) + z = 2014 or 1000w+200x+30y+4z=20141000w + 200x + 30y + 4z = 2014. Each of w,x,y,zw, x, y, z is a single digit and w0w \neq 0. Now ww cannot be 3 or greater, or the left side would be at least 3000, which is too large. Thus, w=1w = 1 or w=2w = 2. If w=2w = 2, then 2000+200x+30y+4z=20142000 + 200x + 30y + 4z = 2014 and so 200x+30y+4z=14200x + 30y + 4z = 14 or 100x+15y+2z=7100x + 15y + 2z = 7. This would mean that x=y=0x = y = 0, which gives 2z=72z = 7 which has no integer solutions. Thus, w2w \neq 2. Therefore, w=1w = 1. This gives 1000+200x+30y+4z=20141000 + 200x + 30y + 4z = 2014 and so 200x+30y+4z=1014200x + 30y + 4z = 1014 or 100x+15y+2z=507100x + 15y + 2z = 507. Since 0y90 \leq y \leq 9 and 0z90 \leq z \leq 9, then 015y+2z1530 \leq 15y + 2z \leq 153. Since 100x100x is a multiple of 100 and 015y+2z1530 \leq 15y + 2z \leq 153, then 100x=400100x = 400 or 100x=500100x = 500 so 15y+2z=507400=10715y + 2z = 507 - 400 = 107 or 15y+2z=507500=715y + 2z = 507 - 500 = 7. From above, we saw that 15y+2z15y + 2z cannot equal 7, so 15y+2z=10715y + 2z = 107, which means that 100x=400100x = 400 or x=4x = 4. Thus, 15y+2z=10715y + 2z = 107. Since 2z2z is even, then 15y15y must be odd to make 15y+2z15y + 2z odd. The odd multiples of 15 less than 107 are 15,45,75,10515, 45, 75, 105. Since 02z180 \leq 2z \leq 18, then we must have 15y=10515y = 105 or y=7y = 7. This gives 2z=22z = 2 or z=1z = 1. Therefore, the integer wxyzwxyz is 1471. Finally, w+x+y+z=1+4+7+1=13w + x + y + z = 1 + 4 + 7 + 1 = 13.

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Source: Omni-MATH, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.