Seems basic, yes, but i honestly don’t know to work it out? 🙂
6 Answers

240/3=80
80, 160, 240.
1/3 of 240 is 80
1/2 is 120
1/4 is 40
Just take 240 and divide by 3 or whatever your after.

Get a ruler in your hands. Measure things until you start to understand how a ruler works. Measure some stuff and figure out where the center is. Say you measure a book and it’s 7/8″ thick. You look at your ruler and see that every eighth is divided into two sixteenths, so obviously half of 7/8″ is going to be 7/16″. If you write that out you have 1/2 x 7/8 = 7/16. And you notice that 1/2 is divided into 2/4 and then into 4/8 and so on, so you can convert anything to anything by multiplying all the numbers on top and then all the numbers on bottom.
Other rulers are divided into 10 and 100 parts. But an inch is still and inch, so anything on one ruler can be translated to the other ruler. A half inch on one ruler is 5/10 or 50/100 on the other. An eighth inch is just 12.5 marks when you have 100 marks per inch. A metric ruler divides an inch into 25.4 parts, so a half inch would be 12.7 of those parts. Pretty simple, isn’t it? Practice this a bit and people will think you went to wizard school.
So you have a ruler with 240 marks and another ruler with 3 marks. How many marks on the one ruler correspond to 1/3 inch on the other? Well, 1/3 inch is 1/3 inch no matter how many marks are in an inch, so you divide 240 by 3 and the answer is 80.

divide 240 by 3 = 80

1/3 * 240/1= 80/1= 80

Divide 240 by the denominator (3) then multiply it by the numerator (1)
Source(s): Maths lessons 
240 divided by 3, the answer will give you one third