Marco walked 27/100 kilometer to the park. then he walked 3/10 kilometer to the library. What fraction of a kilometer did he walk in all?

57/100

Step-by-step explanation:

First, convert 3/10 into hundreths to get a denominator equal to the other:

3/10 km = 30/100km

Add the numerators: 27+30=57

Place numerator over common denominator: 57/100

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

f

step-by-step explanation:

f