52% of 78

Question

52% of 78

P · Accepted Answer

First do half of 78 to get 39. Then double 78 to get 156; change that to 1.56. The final answer is 40.56.

You can find tricks for this sort of thing at arscalcula.com

Dan · Answer

The trick to this is to compare to nice numbers and then use FOIL in your head.

52% is only 2% off from 50% so in your head write 52% = (50%+2%).

Thus 52% times 78 is 78(50%+2%)=(78)(1/2+1/50)= 78/2 + 78/50.

With this mental map in your head you can do easy calculations to get the correct answer.

78/2 = 39 
78/50 = 156/100 = 1.56

Answer: 39+1.56=40.56

Anonymous · Answer

52*78=52*58+52*20=3016+1040=4056, so 40.56

scott · Answer

i love P's approach!
I was thinking half to get 39, then extra 2% left, 2% times 78 is about 1.5, add them and get 40.5, a pretty good approximation.  P's approach is better.

Jane Street

Jane Street Interview Question

Interview Answers

Want the inside scoop on your own company?

Bowls

Followed companies

Job searches