Answer:
= 78
Step-by-step explanation:
Step One:
1 + 4= 5
Step Two:
5+9= 14
Step Three:
14+64= 78
= 78
Hope it helps :)
Answer: 441
Step-by-step explanation:
The formula for an arithmetic sum is
[tex]$\frac{\text{number of terms}}2 \cdot (\text{first term + last term})$[/tex]
We know that the [tex]\text{first term + last term} = -1 + 64 = 63[/tex]. So now all we need is the [tex]\text{number of terms}[/tex]. Well, if you draw each number onto the number line, you get something like
---|------|------|------|------|------|-----|------|-----|------|-----|------|-------|----------
-1 0 1 2 3 4 5 6 7 8 9 10 11 ...
You can see that your numbers are spaced 5 apart, and they go from -1 all the way up to 64. So what you're really asking is, "how many segments of five can I draw from -1 up to 64?" The length of the line from -1 to 64 is 65 (think about it), so the number of line segments is 65/5 = 13. However, we didn't count 64 itself, since there's no line segment past it! So really there are 14 terms in this sequence. Thus the total sum is
[tex]$\frac {14}2 \cdot (63) = \boxed{441}.$[/tex]
