Four habits that save time
A timed arithmetic test is won on the easy questions. Every question you stall on is a question you do not get to.
So skip what stalls you. Move on the moment a question does not open up, and come back to that kind of question later if there is time.
Learn the sign rules. Adding a negative number takes it off. Subtracting a negative number adds it.
Anchor a decimal to a whole number, then adjust. For 4.7 times 8, do 5 times 8 first, then take off 0.3 times 8.
Know the conversions by heart, because interviewers ask for them in other shapes. 1/8 is 0.125, 1/16 is 0.0625, and 2 to the 10 is 1024.
A basis point is one hundredth of one percent. So 25 basis points is 0.25 percent, and 25 basis points of 4,000 is 10.
Four worked at speed
Take −63 + 152. Adding a negative is the same as taking it off, so read it as 152 − 63. That is 89.
Take 4.7 × 8. Anchor to 5: 5 × 8 = 40. You added 0.3 to each of the 8, which is 2.4 too much, so take it off. The answer is 37.6.
Take 174 ÷ 4. Split the dividend where the division is easy: 160 ÷ 4 = 40 and 14 ÷ 4 = 3.5. Add them for 43.5.
Take 15 percent of 240. Ten percent is 24, and half of that is 12. Add them for 36.
One with two minus signs
Here is 56 − (−24).
The second minus sign belongs to the number, not to the operation.
Reading it as a plain subtraction is the usual slip.
Try it
What is 56 − (−24)?
- 80
- 32
Show the answer
80
Correct. The second minus sign belongs to the 24, so the sum to do is 56 + 24, which is 80.
Enable JavaScript to answer interactively and save your place.
Practice Quant interview arithmetic