courses › Mental Arithmetic

Time, rates, and short money stories: pick the operation yourself.

Best in your head · no pen, no calculator why?

Learn first (about 3 minutes)

Opens at level 14.

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Builds on: Bigger multiplication (not open yet) · Money & prices (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.

• Minutes to hours par 7 s not tried yet

  worked example

  How many hours is 45 minutes? Answer as a decimal.

  Answer: 0.75

  1. Minutes are sixtieths of an hour: 45 ÷ 60 = 0.75 hours.

• Rate × time par 10 s not tried yet

  worked example

  At $85 per hour, how much do you earn in 45 minutes?

  Answer: $63.75

  1. 45 minutes is 0.75 hours, and $85 × 0.75 = $63.75.

• Short money stories par 15 s not tried yet

  worked example

  A $381.50 bill is split equally among 7 people. How much does each person pay?

  Answer: $54.50

  1. $381.50 ÷ 7 = $54.50.
  2. Check: 7 × $54.50 = $381.50.

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

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