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?

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.