95
Subtracting from one (practice)
Textbook: Part 3, lesson 95, pp. 75–77
GoalMore practice subtracting from 1: finding the rest; finding the whole when a part is known (with a diagram).
New words
the rest · qolgan qismfinding the whole · butunni topishone share · bitta ulushdiagram · sxema
Explanation
If a part of a whole is known, we find the rest by subtracting from 1: 1 − 3/8 = 8/8 − 3/8 = 5/8. If we also know how big that part is, we can find the whole. For example, 3/5 of a whole is 24. First find one share: 24 : 3 = 8 (that is 1/5). Then find the whole: 8 × 5 = 40. Drawing a segment split into equal parts (a diagram) helps in these problems.
Worked examples
1/3 of the fish in an aquarium are red, and there are 9 red ones. All the fish: 9 × 3 = 27. The fish that are not red make 1 − 1/3 = 2/3.
A hiker has walked 2/5 of the route, which is 16 km: 16 : 2 = 8 km (1/5), the whole route is 8 × 5 = 40 km.
Class activity
“Find the whole”: the teacher colours 2 of 5 parts in a drawing and says they hold 14 items. Children find how many are in one part and in the whole.
Practice
1
3/7 of the trees in an orchard are apple trees. What part are the other trees?
4/7
2
1/5 of the flowers in a flower bed are tulips, and there are 9 tulips. How many flowers are there in all?
45
3
A cyclist has ridden 3/8 of the route, which is 15 km. How many kilometres is the whole route?
40
4
Nilufar has read 2/9 of a book, which is 18 pages. How many more pages must she read?
63
5
Work out 1 − 4/9 − 2/9.
3/9