Its not because of the range of 314e7 and 42e7 is outside float rather their sizes are 64 bit. That's why you can't assign it in float.
For example following is legal.
Here is a quote from JLS 3.0
The largest positive finite float literal is 3.4028235e38f. The smallest positive finite nonzero literal of type float is 1.40e-45f. The largest positive finite double literal is 1.7976931348623157e308. The smallest positive finite nonzero literal of type double is 4.9e-324.
Question is not that whether they are in the range of int or not. 3e1 is definitely in the range of int but still you can't assign it in int. Reason is simple, 3e1 is a double can't be assigned to int.
So you have to cast it in int.
By the way these ranges are not required in exam. Just you need to know ranges of char and integral data types. Nothing more.
Above five ranges are not difficult to remember. Integral types are from...