Correct Answer - a
(a) According to the question,
Amount `= P (1 +(R)/(2 xx 100))^(2 xx t)`
`rArr 68921 = 64000 ( 1+ (5)/(2 xx 100))^(2xxt)`
`rArr (68921)/(64000)= (1+(1)/(40))^(2xxt)`
`rArr ((41)/(40))^(3) = ((41)/(40))^(2xxt)`
`rArr 2t = 3 rArr t = (3)/(2) rArrt = 1(1)/(2)years`