Let the investment at C.I be Rs X Investment at SI = 2/3 X CI = 21X/100 SI=7XT/100 21X/100=50/100*(7XT)/100 T = 6 years Answer - 4) 6 years Explanation: Let the investment at C.I be Rs X Investment at SI = 2/3 X CI = 21X/100 SI = 7XT/100 21X/100=50/100*(7XT)/100 T = 6 years