Question

Twin brothers, Andy and Brian mow their grandparent's lawn together in 12 minutes. Brian could mow the lawn himself in 10 minutes more than it would take Andy. How long would it take each person to mow the lawn alone?

Answer 1

Let
x = time of Byran's work
x + 10 = time of Andy's work

Rate is usually expressed a reciprocal. The total rate will be 12 minutes.
1/x + 1/(x + 10) = 1/12
The value of x will be 20 minutes.

Therefore Byran can take 20 minutes while Andy can take 30 minutes.