I had uninstalled WhatsApp and downloaded the latest version, but after the download I can't install it. I am using a Lenovo A6000. Please tell me what I can do to reinstall the app.
Here, try downloading this and installing it: http://www.apkmirror.com/apk/whatsapp-inc/whatsapp/whatsapp-2-12-373-android-apk-download/. Make sure unknown sources is enabled: Settings > Security > Unknown Sources and confirm the popup. Then just click on the downloaded file and it should install.
It is officially signed so you will be able to receive updates from google play.