In 20 years Mark will be three times as old as he was 10 years ago how old is he

Age of Mark is 25 years.

Step-by-step explanation:

Let the current age of Mark = x years

After 20 years, age of Mark=(x+20) years

10 years ago,age of Mark was (x-10) years.

In 20 years Mark will be three times as old as he was 10 years ago.

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constant acceleration- a

constant velocity- c

no velocity or acceleration- b

explanation:

for body moving with a constant acceleration, the rate of change of displacement changes over time. this is proven by the increasing gradient of the curve (a) against time.

a body that is moving at constant velocity covers equal distances over equal periods of time, thus the straight line with a constant gradient c.

a stationary body   covers no displacement as time elapses. thus the flat line with   zero gradient.