A group of $400$ soldiers has provisions for $31$ days, which represents $400 × 31 = 12,400\displaystyle soldier-days of ration.<br>After $28 days, the ration consumed by the $400× …" style="color:#cc0000">\displaystyle soldiers is $400 × 28 = 11,200 soldier-days.
The remaining ration is:
Remaining Ration=12,400−11,200=400×(31−28)=1,200 soldier-daysAt this point, $280
soldiersarecalledback.Theremainingnumberofsoldiersis:<br><spanclass="katex−display"><spanclass="katex"><spanclass="katex−mathml"><mathxmlns="http://www.w3.org/1998/Math/MathML"display="block"><semantics><mrow><mtext>Remaining Soldiers</mtext><mo>=</mo><mn>400</mn><mo>−</mo><mn>280</mn><mo>=</mo><mn>120</mn><mtext> soldiers</mtext></mrow><annotationencoding="application/x−tex">Remaining Soldiers=400−280=120 soldiers</annotation></semantics></math></span><spanclass="katex−html"aria−hidden="true"><spanclass="base"><spanclass="strut"style="height:0.8889em;vertical−align:−0.1944em;"></span><spanclass="mordtext"><spanclass="mord">Remaining Soldiers</span></span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.7278em;vertical−align:−0.0833em;"></span><spanclass="mord">400</span><spanclass="mspace"style="margin−right:0.2222em;"></span><spanclass="mbin">−</span><spanclass="mspace"style="margin−right:0.2222em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.6444em;"></span><spanclass="mord">280</span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.6944em;"></span><spanclass="mord">120</span><spanclass="mordtext"><spanclass="mord"> soldiers</span></span></span></span></span></span><br>Lettheremainingrationlastfor\displaystyle soldiers are called back. The remaining number of soldiers is:<br><span class="katex-display"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><mtext>Remaining Soldiers</mtext><mo>=</mo><mn>400</mn><mo>−</mo><mn>280</mn><mo>=</mo><mn>120</mn><mtext> soldiers</mtext></mrow><annotation encoding="application/x-tex">Remaining Soldiers=400−280=120\displaystyle \text{Remaining Soldiers} = 400 - 280 = 120Remaining Soldiers=400−280=120 soldiers\displaystyle \text{ soldiers} soldiers</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord text"><span class="mord">Remaining Soldiers</span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7278em;vertical-align:-0.0833em;"></span><span class="mord">400</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">280</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord">120</span><span class="mord text"><span class="mord"> soldiers</span></span></span></span></span></span><br>Let the remaining ration last forsoldiersarecalledback.Theremainingnumberofsoldiersis:<br><spanclass="katex−display"><spanclass="katex"><spanclass="katex−mathml"><mathxmlns="http://www.w3.org/1998/Math/MathML"display="block"><semantics><mrow><mtext>Remaining Soldiers</mtext><mo>=</mo><mn>400</mn><mo>−</mo><mn>280</mn><mo>=</mo><mn>120</mn><mtext> soldiers</mtext></mrow><annotationencoding="application/x−tex">Remaining Soldiers=400−280=120 soldiers</annotation></semantics></math></span><spanclass="katex−html"aria−hidden="true"><spanclass="base"><spanclass="strut"style="height:0.8889em;vertical−align:−0.1944em;"></span><spanclass="mordtext"><spanclass="mord">Remaining Soldiers</span></span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.7278em;vertical−align:−0.0833em;"></span><spanclass="mord">400</span><spanclass="mspace"style="margin−right:0.2222em;"></span><spanclass="mbin">−</span><spanclass="mspace"style="margin−right:0.2222em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.6444em;"></span><spanclass="mord">280</span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.6944em;"></span><spanclass="mord">120</span><spanclass="mordtext"><spanclass="mord"> soldiers</span></span></span></span></span></span><br>LettheremainingrationlastforD$ days for the $120$ soldiers:
120×D=1,200 ⟹ D=10 days120 ×\displaystyle \times× D = 1,200 \implies D = 10 days\displaystyle \text{ days} days120×D=1,200⟹D=10 days