Force = mass x acceleration
but force was halved = 1/2 and mass doubled = 2 ( assuming that force and mass are 1N and 1kg respectively)
f = ma = 12\,\frac{1}{2}21 = 2 x a
dividing both sides by 2
a = 12× 12= 14\,\frac{1}{2} \times \,\frac{1}{2} = \,\frac{1}{4}21×21=41
