How to solve Speed arithmetic questions

Integers, decimals, fractions and percents, typed. Fractions like 7/8 are accepted. This is the Flow Traders and Akuna math test style: skip anything slow.

How to solve them

Add

1. Add left to right: hundreds, then tens, then ones.
2. Round one number and fix up: 486 + 397 = 486 + 400 - 3.
3. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Sub

1. Count up from the smaller number instead of borrowing.
2. Or round the number you subtract: 812 - 297 = 812 - 300 + 3.
3. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Multiply

1. Split one factor into tens and ones, multiply both parts, add.
2. Near a round number: 49 × 23 = 50 × 23 - 23.
3. Around a middle number: (50 - a)(50 + a) = 2500 - a².
4. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Divide

1. Find the tens digit of the answer first, then divide what is left.
2. Halve both sides when you can: 336 ÷ 16 = 168 ÷ 8 = 84 ÷ 4 = 21.
3. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Decimals

1. Multiply as whole numbers, then put the decimal places back.
2. For adding, work in hundredths so there are no decimal points to line up.
3. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Fractions

1. Know eighths and fifths as decimals: 1/8 = 0.125, 3/8 = 0.375, 5/8 = 0.625, 1/5 = 0.2.
2. Add: common denominator. Multiply: tops times tops, bottoms times bottoms.
3. You can type a fraction like 7/8 as your answer.
4. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Percent

1. Find 10% by moving the decimal point, then scale: 35% = 3.5 × 10%.
2. x% of y = y% of x: 4% of 75 = 75% of 4 = 3.
3. Speed tests are reported to cost a point for a wrong answer, so skip anything that would take more than about 8 seconds.

Worked examples

• 50 × 6

  Answer: 300

  1. Split 50 = 50 + 0.
  2. 50 × 6 = 300 and 0 × 6 = 0. Total 300.

• 1224 ÷ 17

  Answer: 72

  1. Tens first: 17 × 70 = 1190.
  2. What is left, 34, is 17 × 2. Answer 72.

• 842 + 530

  Answer: 1372

  1. Add the hundreds first: 800 + 500 = 1300.
  2. Then the rest: 42 + 30 = 72. Total 1372.

Firms that test this

Flow Traders · Akuna Capital · Da Vinci · SIG · Five Rings

All guides