###Human: Jacob can write twice as fast as Nathan. Nathan wrote 25 letters in one hour. How many letters can the two write in 10 hours together?, ### Assistant: Since Nathan writes 25 letters in an hour, Jacob writes 25*2 = 50 letters in an hour.
Together, they write 50+25 = 75 letters in an hour,
In 10 hours, they'll write a total of 75*10 = 750 letters 
 So the answer is :  750