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Bunuel
Vijayeta
Matt is touring a nation in which coins are issued in two amounts, 2¢ and 5¢, which are made of iron and copper, respectively. If Matt has ten iron coins and ten copper coins, how many different sums from 1¢ to 70¢ can he make with a combination of his coins?

A. 66
B. 67
C. 68
D. 69
E. 70

The total sum is 10*2 + 10*5 = 70¢. If you can make each sum from 1 to 70 (1¢, 2¢, 3¢, ..., 70¢), then the answer would be 70 (maximum possible).

Now, with 2¢ and 5¢ we cannot make 1¢ and 3¢. We also cannot make 69¢ and 67¢ (since total sum is 70¢ we cannot remove 1¢ or 3¢ to get 69¢ or 67¢).

So, out of 70 sums 4 are for sure not possible, so the answer must be 70 - 4 = 66 sums or less. Only A fits.

Answer: A.

Hi Bunuel
I understood your explanation but I have a question.
According to the answer options given we got 66 as the answer but sums such as 28, 48 etc. also cannot be formed right..?
If the answer choices would have more lower numbers then we had to consider these sums also..? Am I right..?
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dpo
Bunuel
Vijayeta
Matt is touring a nation in which coins are issued in two amounts, 2¢ and 5¢, which are made of iron and copper, respectively. If Matt has ten iron coins and ten copper coins, how many different sums from 1¢ to 70¢ can he make with a combination of his coins?

A. 66
B. 67
C. 68
D. 69
E. 70

The total sum is 10*2 + 10*5 = 70¢. If you can make each sum from 1 to 70 (1¢, 2¢, 3¢, ..., 70¢), then the answer would be 70 (maximum possible).

Now, with 2¢ and 5¢ we cannot make 1¢ and 3¢. We also cannot make 69¢ and 67¢ (since total sum is 70¢ we cannot remove 1¢ or 3¢ to get 69¢ or 67¢).

So, out of 70 sums 4 are for sure not possible, so the answer must be 70 - 4 = 66 sums or less. Only A fits.

Answer: A.

Hi Bunuel
I understood your explanation but I have a question.
According to the answer options given we got 66 as the answer but sums such as 28, 48 etc. also cannot be formed right..?
If the answer choices would have more lower numbers then we had to consider these sums also..? Am I right..?


Hi dpo

All sums except 1, 3, 67 and 69 are possible. A sum of 28 is formed with 2x5¢ + 9x2¢. 48 is formed by 6x5¢ + 9x2¢. Try any other number, and you will be able to make the sum using the coins available.

Thanks
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Hi Bunuel,

How do we get to a sum of 6c or 11c using the given coins?

TIA
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kindlefire6373
Hi Bunuel,

How do we get to a sum of 6c or 11c using the given coins?

TIA

6¢ = 2¢ + 2¢ + 2¢
11¢ = 5¢ + 2¢ + 2¢ + 2¢
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