Reading a ratio as times, film 1 of 2
Today's question: Adam and Grace tip out all the bottle caps collected in their jars. The number of Adam's…
Questions in this lesson
Transcript
Adam and Grace tip out all the bottle caps collected in their jars. The number of Adam's caps to Grace's is in the ratio 3 to 5. Draw a bar for each of them. Adam's caps first, 3 blue units. Then Grace's caps, 5 blue units, on the bar below. Now write the two names down. Adam to Grace, 3 to 5. That ratio is a comparison. It compares Adam's units with Grace's units. For every 3 caps Adam has, Grace has 5. And that's all it says. Neither number counts all the caps. Now the question changes. What fraction of all the caps are Adam's? A fraction needs a whole, and this question names it. The whole is all the caps. That's both bars together. Adam's 3 units and Grace's 5 units together. 3 plus 5 is 8 units in the whole. So read the fraction off the bars. Adam's caps are 3 of the 8 units in the whole. That's 3 over 8. Adam's caps are 3 over 8 of all the caps. Careful here. 3 to 5 doesn't make it 3 over 5. The 5 is Grace's units. It isn't the whole. The whole is all 8 units. So the fraction is 3 over 8.
Your turn. What fraction of all the caps are Grace's? Read it off the bars. Try it first. Pause if you like. Grace's caps are 5 units. 5 of the 8 units in the whole. So Grace's caps are 5 over 8 of all the caps. Two bars, drawn once. The ratio compares Adam's units with Grace's. 3 to 5. The fraction compares Adam's units with the whole. 3 over 8. The bars didn't change. The question did.