Alex and Freddy collect stamps. The number of stamps in Alex’s collection is in ratio 3:5 to the number of stamps in Freddy’s collection. If Freddy gives Alex 10 stamps, the ratio will change to 7:9. How many stamps are in both collections together?

suppose Alex has 3x stamps, Freddy has 5x stamps. After Freddy gives Alex 10 stamps, Alex has 3x+10 while Freddy has 5x-10
the new ratio is 7 to 9, so we have the equation: (3x+10)/(5x-10)=7/9
9(3x+10)=7(5x-10)
27x+90=35x-70
160=8x
x=20
So Alex has 3*20=60 stamps while Freddy has 5*20=100. Together they have 160