the number of elements in the union of the A sets is:5(30)−rAwhere r is the number of repeats.Likewise the number of elements in the B sets is:3n−rB
Each element in the union (in S) is repeated 10 times in A, which means if x was the real number of elements in A (not counting repeats) then 9 out of those 10 should be thrown away, or 9x. Likewise on the B side, 8x of those elements should be thrown away. so now we have:150−9x=3n−8x⟺150−x=3n⟺50−x3=n
Now, to figure out what x is, we need to use the fact that the union of a group of sets contains every member of each set. if every element in S is repeated 10 times, that means every element in the union of the A's is repeated 10 times. This means that:150 /10=15is the number of elements in the the A's without repeats counted (same for the Bs as well).So now we have:50−15 /3=n⟺n=45
A
this is a geometric sequence since there exists a common ratio r between the terms
r = 
= 
= 
= 3
B
to obtain the next term in the sequence multiply the previous term by 3
= 3 
← recursive rule
C
the n th term of a geometric sequence is
= 
where is the first term in the sequence
= 7 × 
← explicit rule
The measures of the angles in a triangle add up to 180°.
