The total stays the same
Primary 5 total unchanged questions: items only move from one box or person to another, so the total stays fixed and splits into equal units.
Questions in this lesson
Transcript
At first, Chloe had 7 marbles for every 3 marbles Marcus had. Chloe then gave Marcus 24 marbles, and they had the same number each. How many marbles did Chloe have at first? Try it first. Pause if you like. Draw what we know. Chloe has 7 blue units. Marcus has 3 blue units. Now put the two bars end to end. Altogether, that's 10 blue units. 7 units and 3 units make 10 units. Now Chloe gives Marcus 24 marbles. Some of Chloe's marbles move across to Marcus. We don't know how many units that is yet. Nothing was added, and nothing was thrown away. So the total is still 10 blue units. Afterwards, they have the same number each. So those 10 units split into two equal shares. 10 units divided by 2 is 5 units each. So Chloe's last 2 blue units cross over to Marcus. Now look at Chloe. She started with 7 blue units, and she's left with 5. 7 units minus 5 units is 2 units. And those 2 units are the 24 marbles. Now share that 24 between the 2 units. 24 divided by 2 is 12. So 1 unit is 12 marbles. So Chloe had 7 units at first. And 1 unit is 12 marbles. 7 times 12 is 84 marbles. The marbles only moved across. So the total is still 10 blue units, before and after. When things only move from one to the other, the total stays the same.