( {a over b } = {2 over 3 })&nbsp;( {b over c } = {5 over 7 })&nbsp;as b is the common quantity so,&nbsp; we will make its value common on both the ratios.&nbsp;a : b = 2 : 3&nbsp;&nbsp;b : c = 5&nbsp; : 7a : b =&nbsp; ( { 2 imes 5&nbsp; over&nbsp; 3 imes 5&nbsp; } )b : c&nbsp; =&nbsp;&nbsp;&nbsp;( { 5 imes 3&nbsp; over&nbsp; 7 imes 3 } )∴&nbsp; a : b : c&nbsp; =&nbsp; 10 : 15 : 21 Answer