What does the : and also :: in the problem What is X? 2.5:150:20::x

Question

I forgot how to solve a problem like this

Answer 1

: is the same as / or "to"

2:3=2/3=2 to 3

these are ratios

:: is the same as the equal sign (=)

you seem to have the symbols in the wrong places so I'll just guess as to where they belong

2.5:150::20:x

this is read as "2.5 is to 150 as 20 is to x" (2.5 is related to 150 in the same manner that 20 is related to x)

solving...

2.5/150=20/x

cross multiply

2.5x=20*150

2.5x=3000

25x=30,000

x=30,000/25

x=1200

another solution...

multiply 2.5 and 150 both by 8

8*2.5=20

8*150=1200 again