Please, I have a very hard time finding the answer

Source: 2018

Please, I have a very hard time finding the answer

Source: 2018

BigDevil

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.

BigDevil

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 |

TonyX

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