Ms. how bought a bag of rice for dinner. she used 3/5 kg of the rice and still had 2 1/4 kg left. how heavy was the bag of rice that ms. how bought?

Step-by-step explanation:

First  let's look at this with just the whole numbers.  Say someone used 2 kg and had 3 left.  it should be pretty simple to see that you started with 5 kg.  It's basically an algebra problem.  if we say x is the starting amount then x-2 = 3.  You could then solve for x=5.  Now, let's dot he same for your actual numbers.  

x - 3/5 = 2 1/4

x = 2 1/4 + 3/5

Now, to add fractions you need to get the same denominators.  we are just really concerned with 1/4 + 3/5.  Now, you need to knwo you can change fractions.  so 1/4 = 2/8 = 3/12 = 4/16 and so on,  You are basically multiplying the numerator and denominator by the same number.  (1*2)/(4*2) = 2/8.  Now, to make both denominators equal you can multiply one fraction by the other denominator.

1/4 + 3/5

(1*5)/(4*5) + (3*4)/(5*4)

5/20 + 12/20 = 17/20.

So now, back tot he main problem, we are adding 2 1/4 + 3/5 = 2 17/20.  so the starting amount was 2 17/20 kg.

There is another way to add fractions but it is more involved and this always works so this is what I always use.