
Please, I have a very hard time finding the answer
Source: 2018
Please, I have a very hard time finding the answer
Source: 2018
The long candles are in multiples of 5, meaning the total number of long candles will end with a 5, or a 0.
Since there are 21 more long candles than short, the total number of short candles will end with a 4, or a 9.
Multiples of 7 which end with a 4 or 9: 14, 49
Since Eva bought less than 50 candles, logically the number of short candles she bought was 14.
14 + 21 = 35
14 ÷ 7 = 2 boxes -> $5.00
35 ÷ 5 = 7 boxes -> $22.40
Total spent -> 5 + 22.40 = $27.40
PS. The answer is either $27.40 or $29.50, depending on which price you follow. The text said a box of 5 long candles cost $3.20, but the diagram stated the cost at $3.50 per box.
Another way of solving this is simply to guess and check.
But before I start guessing blindly, I would first do a bit of analysing.
The least number of short candles bought is 7.
7 + 21 = 28
So least number of long candles bought would be 30 (smallest number which is multiple of 5, and more than 28)
So I would start my guessing from 30, and stop at 40 since total number of candles is less than 50.
Long Candles | 30 | 35 | 40 |
Short Candles | 30 – 21 = 9 | 35 – 21 = 14 | 40 – 21 = 19 |
Is it multiple of 7? | No | Yes | No |
Short | Long | |
Qty per box | 7 | 5 |
Qty purchased | 7u | 7u+21 |
7u+7u+21=14u+21<50 –>14u<29–>u<2.07
So u can only be 1 or 2
u | Short(7u) | Long(7u+21) | |
1 | 7 | 28 | 28 is not multiple of 5 |
2 | 14 | 35 | 35 is multiple of 5,YES |
$2.5×2+(35/5)*$3.2=$27.4