To make back the investment after a 10% drop, a 11% increase is needed; to make back the investment after a 20% drop, a 25% increase is needed; to make back the investment after a 30% drop, a 43% increase is needed; to make back the investment after a 40% drop, a 67% increase is needed; to make back the investment after a 50% drop, a 100% increase is needed; to make back the investment after a 60% drop, a 250% increase is needed; to make back the investment after a 70% drop, a 333% increase is needed; to make back the investment after a 80% drop, a 500% increase is needed; to make back the investment after a 90% drop, a 1000% increase is needed.