High School Math

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Sunday, April 03, 2005


Cynthia purchased almost 100 stamps today, in three different lots.
Some of her stamps cost 66 cents, some cost $1.68, and some cost $3.08.
She paid exactly the same amount for each lot.
How much did she pay for each lot?
 One possible solution is :
Let the number of stamps in each lot be x, y, z.
Then 66x = 168y = 308z
Factors of 66 are 2x3x11
of 168 are 2x2x2x3x7
of 308 are 2x2x7x11
Common factors of the three are 2x2x2x3x7x11 = 1848
Thus, 66x = 1848k, 168y = 1848k, 308z = 1848k where k is an integer.
Then x = 28k, y = 11k, z = 6k.
Now, x + y + z = 45k.
And, since the number of stamps is almost 100, k must be equal to 2.
Number of stamps in first lot is x = 28x2 = 56.
in second lot is y = 11x2 = 22.
in third lot is z = 6x2 = 12.
Total number of stamps is 56+22+12 = 90.
Value of stamps in first lot is 66x56 = $36.96.
in second lot is 168x22 = $36.96.
in third lot is 308x12 = $36.96.
If you have a shorter solution please submit as guest or comment.

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