Решите 60% класса пошли в кино, а остальные 12 человек - на выставку.сколько учащихся в классе?

Х - 60%
12 --40% х =(12×60):40=18 в кино пошли
всего в классе 18 +12=30 учеников.

100%-60%=40% (человек). - 12 человек. 
40%=12(человек)
12*100%/40%=30(человек)- в классе.
ответ: 30 ЧЕЛОВЕК

6×4=24 км Error occurred in script: WailaPE Mod.js org.mozilla.javascript.WrappedException: Wrapped java.lang.RuntimeException: getName called with invalid item ID: -1 (WailaPE Mod.js#5) at org.mozilla.javascript.Context.throwAsScriptRuntimeEx(Unknown Source) at org.mozilla.javascript.MemberBox.invoke(Unknown Source) at org.mozilla.javascript.FunctionObject.call(Unknown Source) at org.mozilla.javascript.Interpreter.interpretLoop(Unknown Source) at script.modTick(WailaPE Mod.js:5) at org.mozilla.javascript.Interpreter.interpret(Unknown Source) at org.mozilla.javascript.InterpretedFunction.call(Unknown Source) at org.mozilla.javascript.ContextFactory.doTopCall(Unknown Source) at org.mozilla.javascript.ScriptRuntime.doTopCall(Unknown Source) at org.mozilla.javascript.InterpretedFunction.call(Unknown Source) at net.zhuoweizhang.mcpelauncher.ScriptManager.callScriptMethod(ScriptManager.java:278) at net.zhuoweizhang.mcpelauncher.ScriptManager.tickCallback(ScriptManager.java:407) Caused by: java.lang.RuntimeException: getName called with invalid item ID: -1 at net.zhuoweizhang.mcpelauncher.ScriptManager$NativeItemApi.getName(ScriptManager.java:3249) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) ... 10 more

6×4=24 км Error occurred in script: WailaPE Mod.js org.mozilla.javascript.WrappedException: Wrapped java.lang.RuntimeException: getName called with invalid item ID: -1 (WailaPE Mod.js#5) at org.mozilla.javascript.Context.throwAsScriptRuntimeEx(Unknown Source) at org.mozilla.javascript.MemberBox.invoke(Unknown Source) at org.mozilla.javascript.FunctionObject.call(Unknown Source) at org.mozilla.javascript.Interpreter.interpretLoop(Unknown Source) at script.modTick(WailaPE Mod.js:5) at org.mozilla.javascript.Interpreter.interpret(Unknown Source) at org.mozilla.javascript.InterpretedFunction.call(Unknown Source) at org.mozilla.javascript.ContextFactory.doTopCall(Unknown Source) at org.mozilla.javascript.ScriptRuntime.doTopCall(Unknown Source) at org.mozilla.javascript.InterpretedFunction.call(Unknown Source) at net.zhuoweizhang.mcpelauncher.ScriptManager.callScriptMethod(ScriptManager.java:278) at net.zhuoweizhang.mcpelauncher.ScriptManager.tickCallback(ScriptManager.java:407) Caused by: java.lang.RuntimeException: getName called with invalid item ID: -1 at net.zhuoweizhang.mcpelauncher.ScriptManager$NativeItemApi.getName(ScriptManager.java:3249) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) ... 10 more