Arithmetic

Yasmin swims at her local swimming pool.
on one visit she swims 40 lenths.The first length she swims is length 1,the second length is 2 and so on.She swims on her back on length which have number that are multiples of 4 or 5.Calculate the number of lengths that she swims on her back.

Please Guide me how to start this question . No idea to have sum to 40 by taking consecutive increasing numbers.
The given answer is 16, but I could not get it.

Reply 1

DFranklin

The question is basically asking how many of the numbers between 1 and 40 are multiples of either 4 or 5.

There are some slick ways of doing this, but if all else fails, simply list all the numbers that work and count them.

Reply 2

Saad jamil

4,8,12,16,20,24,28,32,36,5,10,15,20,25,30,35 now count them which makes 16 . We didn't include 40 as question says either

Reply 3

DFranklin

Original post by Saad jamil

4,8,12,16,20,24,28,32,36,5,10,15,20,25,30,35 now count them which makes 16 . We didn't include 40 as question says either

As a general rule, resurrecting old posts is frowned upon.

But in this case I'll point out the question does *not* say either, it says "4 or 5", which is pretty unambiguous (although either would be too, to be honest).

40 should be in your list. But note also you have 20 in your list twice. If you don't double count the numbers that appear twice, you'll get 16.

(edited 2 years ago)

Reply 4

SmThN

So you have to get all the multiples of 4 and 5 till 40 which equals to :-
4,5,8,10,12,15,16,20,24,25,28,30,32,35,36,
40.
We don't have to add these but what we have to do is we have to get the number of these.
4 is 1 length, 5 is second length and so on.
If we do that we get 16.
Count em* EZ

(edited 11 months ago)

Reply 5

davros