document.write( "Question 511344: Kristen can finish a task in 5 hours. When Cristina helps Kristen, they can finish the task in 4 hours. How long does it take Cristina to finish the task if she works alone?
\n" ); document.write( " \n" ); document.write( "

Algebra.Com's Answer #342155 by oberobic(2304) $\"\"$ $\"About$

You can put this solution on YOUR website!
Kristen does 1/5 of the whole job per hour.
\n" ); document.write( ".
\n" ); document.write( "Cristina does the the job at an unknown rate per hr: 1/C
\n" ); document.write( ".
\n" ); document.write( "Working together they can do the whole job in 4 hrs.
\n" ); document.write( ".
\n" ); document.write( "(1/5 + 1/C)*4 = 1 whole job
\n" ); document.write( ".
\n" ); document.write( "1/5 + 1/C = 1/4
\n" ); document.write( ".
\n" ); document.write( "1/C = 1/4 - 1/5
\n" ); document.write( ".
\n" ); document.write( "1/C = 5/20 - 4/20
\n" ); document.write( ".
\n" ); document.write( "1/C = 1/20
\n" ); document.write( ".
\n" ); document.write( "Cristina can do the job working alone in 20 hr.
\n" ); document.write( ".
\n" ); document.write( "Check to see if they can do the job in 4 hr working together.
\n" ); document.write( ".
\n" ); document.write( "(1/5 + 1/20)* 4 = ??
\n" ); document.write( ".
\n" ); document.write( "(4/20 + 1/20) *4 = 5/20 * 4 = 1/4*4 = 1
\n" ); document.write( ".
\n" ); document.write( "Correct.
\n" ); document.write( ".
\n" ); document.write( "Answer: Cristina takes 20 hr working alone.
\n" ); document.write( ".
\n" ); document.write( "Done. \n" ); document.write( "

\n" );