Answer:
100 grains of rice in 1 kg rice, using the value of "5 x 10" as correct. Note the comments below.
Explanation:
The expression "5 x 10" seems to missing an exponent for the 10. I suspect there are more than 50 grains of rice in 1 kg, at least on Earth. I will assume 5 x 10 is correct, but will add an exponent of 1 (10^1) to illustrate how the correct exponent can be added to get the correct result.
We can approach this by setting up conversion factors that will convert kg rice to grains of rice.
We are given a 20 kg bag of rice and want to find the grains of rice. The conversion factor should be one that has the units (grains rice/kg rice)/
"There are approximately 5 x 10^1 grains of rice in a one kg bag of rice." provides the information we need: (5x10^1 grains)/(1 kg rice).
We can use this conversion factor in a multiplication step so the kg rice cancels and we are left with only grains of rice:
(20 kg rice)*((5x10^1 grains)/(1 kg rice)) = 100 grains of rice.
Note how the kg rice cancels, leaving just grains rice. If the correct value is 5 x 10^4, then the calculation would be:
(20 kg rice)*((5x10^4 grains)/(1 kg rice)) = 1,000,000 grains of rice.