kate can make a toy in 9 hours and chris can make the same toy in 7 hours. How long would it take them to make the toy if they worked together on it?

Answer 1

Kate can make 1 toy in 9 hours, so in terms of work she can make ¹/₉ toy per hour.

Chris can make 1 toy in 7 hours, so Chris can make ¹/₇ toy per hour.

Together, they can make ¹/₉ + ¹/₇ toy per hour.

¹/₉ + ¹/₇ = ⁷/₆₃ + ⁹/₆₃ = ¹⁶/₆₃ toy per hour.

If we take the reciprocal of that, we can find how many hours it would take per toy, which would be ⁶³/₁₆ hours, or 3 ¹⁵/₁₆ hours.