courses › Pre-Algebra

Scale ratios, split amounts, and compare unit prices.

In your head, jot if needed · no calculator why?

Learn first (about 3 minutes)

Opens at level 19.

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Builds on: Fraction arithmetic (not open yet)

skills · practice stats

From rounds of this course only: box, review and trial answers are left out. Once a skill has 40 tries, it compares your first 20 tries with your last 20.

• Missing term par 11 s not tried yet

  worked example

  1 : 2 = 6 : x. What is x?

  Answer: 12

  1. 1 × 6 = 6, so scale the 2 by 6 as well: x = 2 × 6 = 12.

• Share in a ratio par 14 s not tried yet

  worked example

  Split $374 in the ratio 6 : 5. What is the larger share?

  Answer: $204.00

  1. There are 6 + 5 = 11 parts, so one part is $374 ÷ 11 = $34.
  2. The larger share is 6 × $34 = $204.

• Best buy par 16 s not tried yet

  worked example

  Almonds come in four sizes. Which is the best value per ounce?

  1. 16 oz for $6.72
  2. 8 oz for $3.68
  3. 24 oz for $9.60
  4. 48 oz for $21.60

  Answer: 24 oz for $9.60

  1. Price per ounce: 8 oz → $0.46, 16 oz → $0.42, 24 oz → $0.40, 48 oz → $0.45.
  2. So 24 oz for $9.60 is the best value.

• Scale a rate par 14 s not tried yet

  worked example

  A machine fills 380 bottles in 5 hours. At the same rate, how many bottles does it fill in 10 hours?

  Answer: 760

  1. 380 ÷ 5 = 76 bottles per hour, and 76 × 10 = 760.

rest ladder

Win 3 of your last 4 rounds and the course rests. A win is 90% right, within 2× the round's par. Pass the review when it comes back and the next rest is longer.

1. 1 day
2. 3 days
3. 7 days
4. 14 days
5. 30 days
6. 60 days
7. mastered · every 90 days

your rounds

No rounds yet.