The number of boys in class 51 is 3 times less than the number of girls, and there are 15 girls. How many boys are there?
五1班男生人数比女生人数的2倍少3人，女生有15人，男生有多少人．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 - 3</gadget>
<output>27</output>

<result>27</result>