Geometric series questions

[Guest]

Find the sum of the 50 greatest negative intergers.

What's the starting number??

I got this: Sn=n/2(2a + (n-1)d)
Sn=50/2(2a + (49)-1)





2nd question I find confusing, cuz I don't get it! >.<

A ball is thrown 6.4m into the air. The ball falls, rebounds to 60% of its previous height, and falls again. If the ball continues to rebound and fall in this manner, find the total distance the ball travels until it hits the ground for the fifth time.

Thanks for the math help,
Anna

 

[tkhunny]

The GREATEST Negative Integer would be -1.

Give it another go.

 

[Denis]

A ball is thrown 6.4m into the air. The ball falls, rebounds to 60% of its previous height, and falls again. If the ball continues to rebound and fall in this manner, find the total distance the ball travels until it hits the ground for the fifth time. Thanks for the math help, Anna

60% = .6
1: 6.4 * .6 = 3.84
2: 3.84 * .6 = 2.304
Continue similarly 3 more times.
Don't forget each distance is travelled twice, including the initial 6.4

You can get the 5th distance by formula: 6.4(.6)^5;
and the sum this way: 2[6.4(.6)^0 + 6.4(.6)^1 .... + 6.4(.6)^5],
but I ain't explaining that.