welcome to math with mr. J in this video I'm going to show you how to solve a proportion using cross multiplication and remember proportions are two ratios that are equivalent and in these proportions we have a missing value represented by a variable so again we're going to use cross multiplication in order to solve for that variables value so let's jump into number one here where we have four tenths equals how many twenty fifths so the first thing I'm going to do is draw some arrows to represent my cross multiplication and now I multiply 25 times four is 100 equals ten times n which is just ten n now it's just a matter of solving this one-step equation in order to isolate that N and find its value so let's divide both sides by ten in order to isolate that N and get our answer so 10 divided by 10 would give us a 1 which is just the same thing as 1 times n which is N and a 100 divided by 10 is 10 so N equals 10 so 4 tenths equals 10 25th - how many eighths equals 15 twentieths so I'm going to draw my arrows to represent the cross multiplication 20 times X gives us 20 X and 8 times 15 gives us 120 so now let's isolate our X and find our answer divide both sides by 20 we get x equals six so six eighths equals 15 xx so I'm the number three now where we have nine twelfths equals six and then our variable M there so we need to find m let's draw our lines to represent the cross multiplication nine M or M times nine there equals 12 times six which is 72 so let's isolate our M divide both sides by nine and that will bring us to our answer M equals eight so nine twelfths equals six eight and lastly number four 10 over W equals 5/9 so draw out our cross multiplication nine times ten is 90 and that equals five times W or five W so we wrap up the problem we need to isolate the W divide both sides by 5 and we get W equals 18 so 10 18 equals 5/9 so there you have it there's how you solve proportions using cross multiplication I hope that helped thanks so much for watching until next time peace