One way to find out is to turn the fractions into numbers without fractions, then it's easier to see how far each of them is away from zero. 5 goes into 10, so any number that 10 goes into, 5 goes into as well. So 10*3*7=210 is a number that 3, 5, 7 and 10 all go into, so we multiply each fraction by 210, because we know we can divide the bottom of each fraction into 210 and get a number that's not a fraction: -3*21, -42, 70 and 4*30, giving us -63, -42, 70 and 120. The negative numbers are 63 and 42 away from zero, and the positive numbers are 70 and 120 away from zero. The smallest number of these is 42, which comes from the second fraction, which is -1/5, so -1/5 is closest to zero.