Question

Twin​ brothers, Billy and​ Bobby, can mow their​ grandparent's lawn together in 53 minutes. Billy could mow the lawn by himself in 20 minutes less time that it would take Bobby. How long would it take Bobby to mow the lawn by​ himself?

Answer 1

5353 minutes = 89.22 hours
Maybe the figures should be 53 and 20??

Let's let Billy = A
The formula to use for work problems is
Time = (A*B) / (A+B)

53 = ( (A +20)* A) / (A +20 + A) )
53 = ( A^2 + 20A ) / (2A + 20)
A^2 + 20A -106A -1060
A^2 -86A -1060
A = 96.935
Bobby Mows in 116.935 minutes