Will I be able to travel around India speaking only English?

English works everywhere with people buying and selling things and in the hospitality and tourism business.

Hindi does not work everywhere and seems to not even be respected in the parts of the country (ie most of India) where it is not the primary language. I found very few people helpful in trying to teach me basic Hindi phrases, the opposite that I found everywhere else I've travelled. I put this down to all the areas I was in having a different primary language so a bit like asking somebody in Slovenia or Romania to teach me some Russian.

Having said that I did learn and use the numbers from one to ten and how to order a cup of tea and those seemed to work well (-: (I think it was "mujhe ek kop chai dijiye".

If you only learn one word for India, make it "namaste" - it worked in every part of the country I went to and for me it was the key for to turning the locals from rudely elbowing in front of me at the train booking window to kindly helping me to fill out my forms! This single word seems to show the local people that you are not just another ignorant outsider.

If you are planning on travelling to only places such as Delhi, Bangalore, Mumbai, Chennai and Hyderabad - essentially the metros - English will not be a problem. There is no one language that really works in India. But in most urban areas such as the ones listed above, English will work without any problem. At most "touristy" places too, you are very likely to find someone who speaks in English. For instance, in Rajasthan the guides actually speak a lot of European languages such as French and Spanish.

If you plan to visit the country side (where mostly the vernacular language is spoken) or taking an off beat path, English may not always work. In such cases, it might just help to learn some stock phrases in the local language. But people are generally friendly; if you stop one person for help, a bunch of them will gather together. Someone in the group will definitely understand what you need.

I traveled around Maharashtra (including Mumbai) and Andhra Pradesh and I had no problem getting by with just English. I did try and learn a few phrases in Hindi, Telugu, and Urdu, however, I hardly used any of them. In the few instances where I did try and speak in the native language (e.g., when trying to bargain), I was often met with a blank stare. This was either due to

1. the seller only wanted to haggle in English;
2. the person actually spoke one of the other 100+ languages in India; or, more likely
3. I completely butchered the pronunciation!

English works, better than Hindi in the southern states. If you are planning to visit cities, English will not cause any problems. Most people on the streets definitely will understand the gist of your question.