Rounding to estimate the difference of 18.14 - 9.88

18.14 rounds to 18 because you look at the 1 and (0, 1, 2, 3, 4) tell you to round down.  That means 18.14 rounds down to 18

9.88 rounds to 10 because you look at the first 8 and (5, 6, 7, 8, 9) tell you to round up.  That means 9.88 rounds up to 10.

Now it's just simple math.  18-10 = 8

Step-by-step explanation:

< xcy ≅ < xby

step-by-step explanation:

in δcax and δbax,

so, δcax ≅ δbax (side-angle-side or sas)

since δcax ≅ δbax, we can conclude < acx ≅ < abx

in δacy and δaby,

so, δacy ≅ δaby (side-angle-side or sas)

since δacy ≅ δaby, we can conclude < acy ≅ < aby

now,

< acy ≅ < aby

=> < acx + < xcy ≅ < abx + < xby

=> < acx + < xcy ≅ < acx + < xby   (since < acx ≅ < abx already proved above)

subtracting < acx from both sides, we get

< acx + < xcy -< acx ≅ < acx + < xby -< acx

cancelling out < acx and -< acx from both sides, we get

< xcy ≅ < xby (proved)