\(\therefore {S_1} = \frac{1}{2}a{(10)^2} = 50a\) .....(i)
\(As\;\;v = u + at\)
\(\therefore \) velocity acquired by particle in \(10 \,sec\) \(v = a \times 10\)
For next \(10\, sec\) ,
\({S_2} = (10a) \times 10 + \frac{1}{2}(a) \times {(10)^2}\)
\({S_2} = \) \(150a\) .....(ii)
From (i) and (ii)
\({S_1} = {S_2}/3\)