Question

A student must leave for campus in 10 mins or he will be late for class. Unfortunately he is snowed in. He can shovel the driveway in 20 mins and his brother can shovel it in 12 mins. If they shov3l together how long will it take to ckeaer the driveway? Will it give him enough time to get to campus ?

Answer 1

Since if he gets the driveway done in 20 minutes he gets 1/20th of the driveway done in 1 minute (if x=20 then x/20=1 by dividing both sides by 20) and if his brother gets 1/12th of the driveway done in one minute, then if t represents the time it takes to shovel the driveway, t/20+t/12=1 driveway shoveled as 1/20+1/12=amount they can do in 1 minute, so t/20+t/12 is how much they can do in t minutes. Multiplying both sides by 20*12=240, we get 12t+20t=32t=240. Dividing both sides by 32, we get 240/32=7.5 minutes to shovel the driveway.