The velocity- time graph of a body is shown in fig.  The ratio of the ........during the intervals OA and AB is .........

Average veloctiy for an interval t is given by area under the curve divided by the time t.

For interval OA, V_av = (1/2 OA x AC)/OA = AC/2

For interval AB, V_av = (1/2 AB x AC)/AB = AC/2

As the area under OCA and BCA are equal the ratio of average velocities are 1:1.