# a level maths sequences question help

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Thread starter 1 month ago
#1
stuck on part b
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1 month ago
#2
(Original post by o_reo)
stuck on part b
Post what you've done so far.
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Thread starter 1 month ago
#3
(Original post by Muttley79)
Post what you've done so far.
well I know this isn't right but what I originally did was say 41/50 was the common ratio and just put it into the sum to infinity = a/(1-r) where a=d and then I got 5 and 5/9 d
so I did it wrong but not sure what Im meant to do as they dont give any other information
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1 month ago
#4
Remember that when it bounces it travels twice the height of the bounce because it has to go up then back down again
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1 month ago
#5
(Original post by o_reo)
well I know this isn't right but what I originally did was say 41/50 was the common ratio and just put it into the sum to infinity = a/(1-r) where a=d and then I got 5 and 5/9 d
so I did it wrong but not sure what Im meant to do as they dont give any other information
Think about it a bit more - you drop it from a certain height it bounces up and then goes back down - so you want total distance ...

d ------------ + 41d/50 + 41d/50 + ...
initial drop + first up + first down + second up etc
Last edited by Muttley79; 1 month ago
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Thread starter 1 month ago
#6
(Original post by Muttley79)
Think about it a bit more - you drop it from a certain height it bounces up and then goes back down - so you want total distance ...

d ------------ + 41d/50 + 441d/50 + ...
initial drop + first up + first down + second up etc
so what would the common ratio be
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1 month ago
#7
(Original post by o_reo)
so what would the common ratio be
Without working it out, I assume your initial common ratio for the bounce heights, of 41/50, is correct. You need to massage the sum slightly to get it into the form of a geometric progress plus/times a couple of bits.

Muttley79 had a typo, and your sum would be:

Last edited by ghostwalker; 1 month ago
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Thread starter 1 month ago
#8
(Original post by ghostwalker)
Without working it out, I assume your initial common ratio for the bounce heights, of 41/50, is correct. You need to massage the sum slightly to get it into the form of a geometric progress plus/times a couple of bits.

Muttley79 had a typo, and your sum would be:

ok thank you!! I get it now
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