The school bought 1,800 books and distributed them to the fourth, fifth, and sixth grades according to the ratio of 4:5:6. How many books were allocated to the sixth grade?
学校买来1800本图书，按4：5：6分给四、五、六年级，六年级分到多少本图书？
<gadget id="calculator">4 + 5 + 6</gadget>
<output>15</output>

<gadget id="calculator">6 / 15</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1_800 * (2/5)</gadget>
<output>720</output>

<result>720</result>