Answer:a=920
Step-by-step explanation: X : Y =Z (R) ; Z< Y
a : 25= x(r=20) ; 20<x
a:45= y(r=20) ; 20<y
a:60=z (r = 20); 20<z
a=25x+20(1)
a=45y+20(2)
a=60z+20(3)
(1);(2);(3)⇒a-20 ∈ [25,45, 60]
25=5²
45=3²x 5
60=2²x 3 x 5
[25, 45, 60]=2²x 3² x 5²=900⇒
⇒a-20∈{0, 900, 1800, ...., 900K}/+20
a ∈ {20, 920, 1820,....., 920K}
a=920
920: 25=36 (r=20)-True=>
a=920 is the smallest number that divided by 25, 45 , 60 leaves a remainder of 20