Albus Dumbledore keeps 274 dragon lizards in his terrarium in Hogwarts. One day he removes two thirds of the male lizards from the terrarium; it is easy for him to tell the males apart from the females since each male has 12 spikes and each female has 4 spikes. How many spikes are left in the terrarium?
There are exactly
1096 spikes left. It doesn't matter how many males or females there are, because the males have 3 times as many spikes as the females. 1/3 of the males remain, and all of the females remain. This averages to 4 spikes per original dragon lizard, which give us 274*4=1096.
Although mfc32 answer is correct I'd like to add a more mathematical approach:
F = number of females in the beginning
M = number of males in the beginning
S = number of spikes in the end
F + M = 274
S = 4 * F + (1/3) * 12 * M
S = 4 * F + 4 * M
S = 4 * (F + M)
S = 4 * 274 = 1096