1) cross multiply: 428x=107y, so x/y=107/428
2) if a=1,b=2,c=4, they're equal, if not then they'ren't equal, so can't be determined
3) 3/r+4/t=3t+4r/rt, so compare that to 3t+4r/r+t, if r or t is less than 1, than the latter is greater, if r and t are both greater than 1, than the former is bigger, can't be determined
4) 15-5 is the distance between 5 and 15, which is 10, if the number is 'x' away from 15, then it is '2x' away from 5, 'x' + '2x'=10, so x=3 and 1/3, 15-3 1/3= 11 2/3.
5) Just draw a mental picture, at the diameter, the longest chord in an circle, consider the distance from the center as 0, the further you move away from the center, the shorter the chords get, this is only true under the assumption of perpendicularity, otherwise, the question makes little sense. so since chord XY is closer, it must be the longer chord.