LM wrote:
If each term in the sum \(a_1+a_2+a_3+...+a_n\) is either 7 or 77 and the sum equals 350, which of the following could be equal to n?
A. 38
B. 39
C. 40
D. 41
E. 42
n=x+y
7x+77y =350
x+y = 10k =n
since last digit of 7x+77y=350 is 0
Only 40 satisfies this condition.
IMO C
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