Ok, so Kumar asked:
What difference do you find between
1= He did it last Sunday.
2= He did it on last Sunday.
Not using the word “on” makes the word “last” act as a preposition. A time marker such as “last”, “since” or “for” can be used as a preposition with nouns. I believe the following will explain this further:
Deletion of preposition is obligatory “when the temporal noun phrase contains a determiner used deictically (i.e.,as seen from the perspective of the speaker such as last, next, this) or when the head noun of the noun phrase contains before, after, next, last or this as part of its meaning (e.g., yesterday, tomorrow, today, tonight)”
source:The Grammar Book:An ESL/EFL Teacher’s course (2nd edition). P.P 404
The second question from Kumar was:
The stock has grown 10%. Vs The stock has grown by 10%.
In this instance, “grow by” is used as a phrasal verb, ie, an idiomatic phrase where the verb is followed by a preposition. Both your sentences are correct, but I would say the second sentence is correct to a greater degree. The first arguably means that the stock value has grown 10% from zero, but the second might mean there has been a 10% increase over a previous figure. In any case, both these examples use the word “grow” as an intransitive verb to mean “expand” or “increase” but the second sentence becomes more specific with the inclusion of the preposition “by”.
And, the third clarification Kumar asked for is:
You save money. Vs You save on money
To save money is to keep it for use later, especially when you will add more money to the existing amount. For example, I have saved enough money to buy a computer.
To save on money is to use just enough cash so you do not waste any. For example, You’ll save on a lot of money if you simply took the train instead of a flight to Denver. Please note that in this case, you are only talking about money that you do not want to waste. “Save on” has nothing to do with keeping money away for a rainy day or adding to it.
Phew, I hope that this will be enough. I am guessing though, that I have more questions coming my way from you again. So my planned entries will have to wait I think. Apologies to the others!