Maths tip:

Some rate questions asks for combined rate. For these, first determine the rate, and then add them together.

Example: "Lionel would take 8 days to build a wall. For the same wall, Nick would take 6 days. How many days would be needed to build the same wall if both of them worked together?"

Lionel rate = 1/8 wall per day

Nick rate = 1/6 wall per day

Combined rate = 1/8 + 1/6 = 3/24 + 4/24 = 7/24 of a wall per day.

For one wall, time taken = 1 / (7/24) = 24/7 days.

To quickly check, notice that 2 of Lionel will take 4 days, and 2 of Nick will take 3 days, so Lionel and Nick will take between 3 and 4 days.