Answer
In 1 set, they will be lifting the same weight.
They will be lifting the same weight when they are both lifting 21 kilograms.
Explanation
Cody starts with 19 kilogram bar and increases this by 2 kilograms on each set.
In n sets, Cody will be lifting (19 + 2n) kilograms.
His partner, starts with 20 kilogram bar and increases this by 1 kilogram on each set.
In n sets, his partner will be lifting (20 + n) kilograms.
We are then asked to calculate when they will be lifting the same kilograms of weight.
When the amount of weight they are lifting becomes the same, we have,
19 + 2n = 20 + n
2n - n = 20 - 19
n = 1
So, in 1 set, they will be lifting the same weight.
when n = 1,
19 + 2n = 19 + 2(1) = 19 + 2 = 21 kilograms.
So, they will be lifting the same weight when they are both lifting 21 kilograms.
Hope this Helps!!!