Mr. A lends 40% of sum at 15% p.a. 50% of rest sum at 10% pa. and the rest at 18% pa. rate of interest. What would be the rate of interest if the interest is calculated on the whole sum?

Explanation:

Let the amount be Rs.x

Investment is done as given below.

Amount left = x−40\100x=60x\100

40\100x at 15% p.a.

50\100of 60x\100=30x\100 at 10% p.a.

Rest amount

=x−40x\100−30x\100=3x\100 at 18% p.a.

Interest earned by each at end of 1 yeas

By 1st => 15\100×40x\100=60\1000x

By 2nd => 10\100×30x\100=30\1000x

By 3rd => 18\100×30x\100=54\1000x

Total interest = 144\1000x

Therefore, Rate % = 144x\1000\x×100 = 14.4%