I am assuming they both keep eating til its gone. So, one guy eats twice as fast, so he can eat two thirds of the pizza by the time guy no2 eats one third.
It takes the first guy ten minutes to eat a whole pizza - 600 seconds. Multiply that by 2/3 gets you 6 mins 40 seconds
I solved it in post above. Yours is wrong sorry - 5 minutes? After 5 minutes, guy number one can eat half a pizza. Guy 2 eats half the speed of him, so you still got 1/4 of a pizza left.
in 1 min the fisrt guy eats the 1/10th of the pizza and
in 1 min the second guy eats ther 1/20th of the pizza
so in 1 min they both eat 1/10 + 1/20 = 3/20 of the pizza
so the whole pizza (20/20) will be eaten in 20/20 : 3/20 = 6,66... minutes!!!
You expected any less? What throws me usually is I expect them to be trick questions... I should assume it is a simple math question first and be done in half the time!
another: outside a room are 3 switches. Just one of them turns-on the light inside the room.
we are outside the room and we can get into the room just once to check!
how can we manage to find out which switch turns-on the light?
p.s. there isn't any window or another way to see what's going on inside the room!