
Akshit S. answered 09/10/15
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Assume that he lends amount 'x' at 16%.
=> Amount lend at 19% = 1,000,000 - x
He wants to obtain average of 18% per year, i.e, 0.18* (1,000,000) -Eqn (1)
Amount obtained from lending at different rates = Amount obtained from 16% + Amount obtained at 19%
= 0.16 * x + 0.19 * (1,000,000 -x) -Eqn(2)
By (1) and (2), => 0.18* (1,000,000) = 0.16 * x + 0.19 * (1,000,000 -x)
=> 0.03 x = 0.01 * (1,000,000)
=> x= 333,333.33 $
ALTERNATE: Assume a see- saw as : 16-------18---19
where, 18 is the balance and 16 and 19 are two ends.
Total weight at 16 and 19 is 1,000,000.
Assuming 'x' at 16, weight at 19 would be '1,000,000 -x'.
So by weight law, (Weight at 16) * Distance of 16 from center balance = (Weight at 19) * Distance of 19 from center balance
=> x* (18-16) = (1,000,000-x) * (19-18)
which yields the same equation
Hope this help.
Cheers !