The average of five numbers is 26. The average of first two numbers is 30 and that of the last two numbers is 7. What is the third number ?
Let the numbers be $$A_1 , A_2 , A_3 , A_4 , A_5$$
=> $$A_1 + A_2 + A_3 + A_4 + A_5 = 26 * 5 = 130$$
Also, $$A_1 + A_2 = 30 * 2 = 60$$
and $$A_4 + A_5 = 7 * 2 = 14$$
=> $$A_3 = 130 - 60 - 14 = 56$$
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