Answer:
4600
Step-by-step explanation:
This is an arithmetic sequence with common difference d between consecutive terms.
d = - 2 - (- 6) = 2 - (- 2) = 6 - 2 = 4
The sum to n terms of an arithmetic sequence is
=
[ 2a + (n - 1)d ]
where a is the first term
here a = - 6, d= 4 and n = 50, hence
=
[ (2 × - 6) + (49 × 4) ]
= 25 ( - 12 + 196 )
= 25 × 184
= 4600
Answer:
The rate of the current is 2 miles per hour.
Step-by-step explanation:
Let us assume that the rate of the river is v miles per hour.
The speed of the boat is 12 miles per hour.
Let us assume also that the boat can go 21 miles in t hours in the downstream and 15 miles upstream at the same time i.e. t hours.
So, from the condition given we can write that
......... (1), and
......... (2)
Now, adding those two equations we get
⇒ hours
Now, from equation (1), we get,
⇒ v = 2 miles per hour
Therefore, the rate of the current is 2 miles per hour. (Answer)
