The average of five positive numbers is 470. The average of first two numbers is 720 and the average of the last two numbers is 150. What is the third number ?
Let the numbers be $$A_1 , A_2 , A_3 , A_4 , A_5$$
=> $$A_1 + A_2 + A_3 + A_4 + A_5 = 470 * 5 = 2350$$
Also, $$A_1 + A_2 = 720 * 2 = 1440$$
and $$A_4 + A_5 = 150 * 2 = 300$$
=> $$A_3 = 2350 - 1440 - 300 = 610$$
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