UPSC CDS 1 2021 Math Paper

We check all option 2∕3,3∕4,4∕5,5∕6
(1) 2∕3 added 3 both numerator and denominator =(2+3)∕(3+3)=5∕6
Change =5∕6−2∕3=(5−4)∕6=1∕6
(2) 3∕4 added 3 both numerator and denominator (3+3)∕(4+3)=6∕7
Change =6∕7−3∕4=(24−21)∕28=3∕28
(3) 4∕5 added 3 both numerator and denominator (4+3)∕(5+3)=7∕8
Change =7∕8−4∕5=(35−32)∕40=3∕40
(4) 5∕6 added 3 both numerator and denominator (5+3)∕(6+3)=8∕9
Change =8∕9−5∕6=(16−15)∕18=1∕18
Hence, required minimum change in 5∕6