Many job tests ban calculators: cognitive aptitude tests similar in format to the CCAT or the Wonderlic, and the arithmetic screens some trading firms use. You get seconds per question, so the method matters more than talent.
Three moves cover most sums:
- Round and adjust. 47 + 38 is 47 + 40 − 2 = 85, and 503 − 178 is 503 − 180 + 2 = 325.
- Split by place value. 23 × 7 is 20 × 7 + 3 × 7 = 140 + 21 = 161.
- Halve and double. 16 × 25 is 8 × 50, which is 4 × 100 = 400.
Work left to right and keep a running total in your head. Get each set right without a clock first, then race it. Speed comes from repetition, so a few short drills on different days beat one long session.