In order to enrich the life of the students after school, the school has strengthened physical exercise and bought a total of 70 basketballs, footballs, and table tennis balls. The ratio of the number of basketballs to footballs is 2:3, and the ratio of footballs to table tennis is 4:5. How many table tennis balls did the school buy?
学校为丰富同学们课余生活加强体育锻炼，买来篮球、足球、乒乓球共70个，买来篮球与足球的个数比是2：3，足球与乒乓球的个数比是4：5，学校买来乒乓球多少个．
<gadget id="calculator">8 + 12 + 15</gadget>
<output>35</output>

<gadget id="calculator">15 / 35</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">70 * (3/7)</gadget>
<output>30</output>

<result>30</result>