One thing that was on my mind this week was what to do when a question gives you 2 T1’s and 2 differences. I learned today that the answer is actually quite simple!
The 1st thing you want to do is list out what you about the question. An example would be to list out the T1’s, the differences, the Sn or Tn and finally the N itself.
The question I will use to get an understanding is a word problem (which typically harder for me to understand).

“As part of a new training routine, Aria does some burpees and push-ups. On the first day she does eight burpees and ten push-ups. Each day she increases the number of burpees by 3 and the number of push-ups by four. What is the total number of burpees and push-ups that she has done at the end of the 20th day?”

As I said earlier it is easier to list out what you know to start your solving! 1. you know that she starts with 8 and 10 burpees and push-ups, this is our T1’s (yes, both) 2. our difference is 3 and 4, we know this because it is implied that she increase the amount she has done by 3 and 4 everyday. 3. N=20, we use 20 as finishing point to but an end to where she is.

T1 = 8 and 10
D = 3 and 4
N = 20

This is how we start with solving the answer. (Sn = n/2(2 * T1 + (n-1)d)
We will start by using the first few numbers that are given to us.

S20 = 20/2(2*8+(20-1)3)
S20=10(57+16)
S20=730

This gives us the answer to the 1st part of our final solution, we will now do the same but with the other numbers provided to us.

S20=20/2(2*10(20-1)4)
S20=10(76+20)
S20=960

Now that we have our 2nd part of our final solution, the final step is simply to add the two final answers of each equation!

730+960
S20=1690.