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How many numbers from 1 to 36 are co-prime to 36?

Competition practiceNumber System, HCF & LCM

A12
B18
C24
D11

Step-by-Step Solution

36 =

2^{2} \times 3^{2}

. Euler's count:

36 \times (1 - \frac{1}{2}) (1 - \frac{1}{3}) = 12

. They are 1, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 35.

Answer: A) 12

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