The velocity-time graph of a body moving in a straight line is shown in figure.

The ratio of displacement and distance travelled by the body in time 0 to 10 s is

look at the v-t graph as areas of rectangles

area above time axis → positive displacement
area below time axis → negative displacement

now take each interval one by one

from 0 to 2 s
velocity = +8 m/s (constant)
so displacement = area = 8 × 2 = 16

from 2 to 4 s
velocity = −4 m/s
so displacement = −4 × 2 = −8

from 4 to 8 s
velocity = +4 m/s
so displacement = 4 × 4 = 16

from 8 to 10 s
velocity = −4 m/s
so displacement = −4 × 2 = −8

now combine properly

net displacement = 16 − 8 + 16 − 8 = 16

distance is different → here we don’t cancel signs
we take total path length

distance = 16 + 8 + 16 + 8 = 48

so finally

ratio = displacement / distance = 16 / 48 = 1/3

idea to remember
displacement = signed area
distance = total area (ignore sign)