the simple interest and the true discount on a certain sum for a given time and at a given rate are rs. 90 and rs. 80 respectively. the sum is:	Choose the correct answer: A) 1360 B) 1450 C) 720 D) 1800 E) none
<gadget id="calculator">90 * 80</gadget>
<output>7_200</output>

<gadget id="calculator">90 - 80</gadget>
<output>10</output>

<gadget id="calculator">7_200 / 10</gadget>
<output>720</output>

<result>C</result>
the simple interest and the true discount on a certain sum for a given time and at a given rate are rs. 90 and rs. 80 respectively. the sum is:
divide(multiply(90, 80), subtract(90, 80))
"sol . sum = s . i . * t . d . / ( s . i ) - ( t . d . ) = 90 * 80 / ( 90 - 80 ) = rs . 720 . answer c"