The third term of a sequence is 19 and the fifth term is 11.
The term-to-term rule is 'Subtract a mystery number.'
What is the first term of the sequence ?
What is the mystery number?
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u3 =19
u5 = 11
assuming the sequence is arithmetic progression
un = u1+(n-1)d
u3=u1+ 2d =19
u5 = u1+ 4d = 11
u5-u3
=2d = -8
d=-4
common difference = -4
u5 = u1+4×(-4) = u1-16 =11
u1 = 11+16 = 27
first term =27
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