What formula do I use for this word problem of

Question

Sheila mixed 3 oz of blue paint and 2 oz of yellow paint. She decides to create 20 oz of the same mixture. How many oz of the yellow paint does Sheila need for the new mixture. What is the formula for the Word problem

Answer 1

You should NOT ask for a magical formula.  The PROCESS to be followed in a problem of this type is illustrated below.

 

Sheila has a mixture 5 oz in total, consisting of 3 oz of blue paint and 2 oz of yellow paint. 

All you have to do is recognize that she must multiply everything by 4, because 20/5 = 4.

 

This gives mixture 20 oz in total, consisting of 15 oz of blue paint and 8 oz of yellow paint. 

 

This is equivalent to the method of proportions, which you may be learning about at this time in school.