The arithmetic mean of ten boys is 8 years, 6 months one of them is 13 years old. then the arithmetic mean of remaining 9 boys is
a)9.5 b) 9 c) 8 d) 7

1. ∠1 is complementary to ∠2 and ∠3 is complementary to ∠2. subtraction property of equality 2. m∠1 + m∠2 = 90 and m∠3 + m∠2 = 90 substitution 3. m∠1 + m∠2 = m∠3 + m∠2 definition of complementary 4. m∠1 = m∠3 given