2) a,$1/2=2/4$ b,$5/7=10/14=15/21$
3) a) Ta thấy :$22/55=11.2/11.5=2/5$ , $26/65=13.2/13.5=2/5$
Do đó : $22/55=26/65$
b) $114/122=57.2/61.2=57/61 , 5757/6161=57.101/61.101=57/61$
Do đó :$114/122=5757/6161$
4)
a, $125/1000=1/8$
b,$198/126=11/7$
c,$3/243=1/81$
d,$103/3090=1/30$