Mental math: .25 + .45 + .65 + .85 +....+1.45=___The answer is 5.95. What is the best way to derive this mentally?
Since each term in the sum is 0.2 higher than the term before it, we have the total sum:
for a total of 7 terms. I find the 0.05 for each part to be annoying, so that's a total of 0.35, with the rest of the sum as
Now, I add in groups of 1.0, so think in pairs:
with the last one getting its own group
This means when we add this up, we end up with
The total sum is 5.95