Rob is saving to buy a new mp3 player. for every $16 he earns babysitting, he saves $7. on saturday, rob earned $48 babysitting. how much money did he save?

50 in 1.5 hours.

Step-by-step explanation:

If Joan can do 50 in 3 hours, then in 1 hour, that’s 50/3.  

Jill completes the rest of the 50, so 50-(50/3) is how many letters Jill can type in an hour.  

50-(50/3)=(150/3)-(50/3)=100/3 letters in an hour. If Jill can write 100 letters in 3 hours, then she can write 50 in 1.5 hours.