Idea 22of 22Builds onFrom kilometres back to the map
Use the whole to find a part
How many orange counters are in 27, at 4 orange for every 5 blue?
Today you'll discover
- how big one group of the ratio is
- how many groups make the whole
- how to find each part
Think first27 counters: 4 orange for every 5 blue
How many of the 27 counters are orange?
Decide first, then press Next. Find the size of one group first.
27 grey counters, not yet sorted. Then they slide into three dashed boxes, each with 4 orange circles and 5 blue squares. Under them: orange to blue equals 12 to 15, the same as 4 to 5; then orange to all equals 12 to 27 and blue to all equals 15 to 27. The last step shows 28 counters at 2 orange for every 5 blue.
See the whole ideathe big idea and the key word, in one place
The big idea
Add the terms to find one group, then count how many groups make the whole.
In a classA class of 30 has 2 girls for every 3 boys. A group is 5 students, so 6 groups: 12 girls and 18 boys.
Easy to get wrongThe 27 is the whole, not the orange or the blue. Compare the whole with one whole group, 4 + 5 = 9.
Key word
- ratio group
- one copy of a ratio's parts together; in 4 : 5 a group is 4 + 5 = 9
Ready to use it?
- Find a part from the whole and a ratio.
- Find the size of one group of a ratio.