Question 1197195
<font color=black size=3>
@josgarithmetic has the right idea, but you'll need to round up to the nearest multiple of 5.


The answer is <font color=red>70 minutes</font>.


70/5 = 14 yo-yo's are made by machine A
70/10 = 7 yo-yo's are made by machine B
That gives a total of 14+7 = 21 yo-yo's


We won't be able to land on 20 exactly, but it's better to go over the goal than come up short.


At the 65 minute mark,
65/5 = 13 yo-yo's are made by machine A
65/10 = 6.5 = 6 yo-yo's are made by machine B
giving a total of 13+6 = 19 yo-yo's 
An extra 1 minute and 40 seconds will not be enough time for either machine to produce that final yo-yo needed.
</font>