if bobby can pitch 21 baseballs in 3 minutes how long will it take him to pitch 15?

Question

I need help finding what the equation would look like. I have trouble setting up word problems which cause the whole problem to be wrong.

Answer 1

The equation involves ratios and proportions so it would look something  like this:

 

Baseball's over minutes  

 

21/3 = 15/x   X is the unknown  value we are solving for (minutes)

                      

21/3=15/X

 

Step  1: cross multiply the fractions

 

   (21•x)=(15•3)

        21x=45

 

Step 2: solve for x 

 

        21x=45 (divide  both sides by 21)

       21/21x=45/21

           X=2 1/7

Answer 2

First find out how many baseballs per minute Bobby can pitch:

Number of baseballs per minute is 21/3 = 7 baseballs/minute

 

You need to determine how many minutes it will take him to

pitch 15 balls:

 

(7 balls/min)(x min) = 15 baseballs

 

x = 15/7 = 2 1/7 minutes

 

If you need to know how many seconds 1/7 minutes is

just multiply by 60 sec/min

 

(1/7 min)(60 sec/min) = 8.6 seconds

 

Time:  2 minutes 8.6 seconds

************************************

You can also set this up as a simple ratio

 

(21 balls)/(3 mins) = (15 balls)/(x min)   cross multiply

21x = 3(15)

21x = 45

x = 45/21

x = 2 3/21

x = 2 1/7 mins