Convert 20°C to Fahrenheit

Question

Solve in your head. What is 20^\circC in Fahrenheit? Aim: under 5 seconds.

Accepted Answer

Exactly: F = 	frac95 C + 32 = 1.8 	imes 20 + 32 = 36 + 32 = 68^\circF. The fast approximation is "double and add 30": 2 	imes 20 + 30 = 70^\circF, close, but 2^\circ high here. Takeaway. "Double and add 30" is quick but overstates because the true multiplier is 1.8, not 2. The two rules agree near 10^\circC; above that the shortcut reads increasingly hot (about 2^\circ high at 20^\circC, 3^\circ at 30^\circC). For accuracy, use 	imes 1.8 + 32.

Convert 20°C to Fahrenheit

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