Question

Subtract
$\left( A \right)$ $6$ hours $10$ minutes $-$ $2$ hours $35$ minutes
$\left( B \right)$ $3$ hours $5$ minutes $-$ $45$ minutes
$\left( C \right)$ $10$ hours $35$ minutes $-$ $1$ hour $55$ minutes
$\left( D \right)$ $4$ hours $20$ minutes $-$ $3$ hours $40$ minutes

Answer 1

Hint: At first, we convert all the hours into minutes and then perform the operation in minutes. This becomes easier as it is simple arithmetic subtraction. At last, we convert all the minutes which have exceeded $60$ , back to hours and minutes format.

Complete step by step solution:
Subtraction of time can be done in the simplest way by converting all the units in the minimum units of the entire expression. Having done so, we will be left with time operations of a single unit. This can be done easily by considering only the values. After that, we will convert back the small units into their original units. For example, if we have to subtract $a$ hours $b$ minutes from $c$ hours $d$ minutes, we do so by converting $a$ hours $b$ minutes to $\left( 60a+b \right)$ minutes and $c$ hours $d$ minutes to $\left( 60c+d \right)$ minutes and then perform the subtraction.
$\left( A \right)$ $6$ hours $10$ minutes is equal to $\left( \left( 60\times 6 \right)+10 \right)$ minutes as one hour is equal to $60$ minutes. $\left( \left( 60\times 6 \right)+10 \right)$ minutes means $370$ minutes. $2$ hours $35$ minutes is equal to $\left( \left( 60\times 2 \right)+35 \right)$ minutes which is equal to $155$ minutes. Thus,
$6$ hours $10$ minutes $-$ $2$ hours $35$ minutes
$=370$ minutes $-155$ minutes
$=215$ minutes
$215$ minutes upon dividing by $60$ gives $3$ as quotient and $35$ as remainder.
Therefore, we can conclude that $6$ hours $10$ minutes $-$ $2$ hours $35$ minutes is equal to $3$ hours $35$ minutes.
$\left( B \right)$ $3$ hours $5$ minutes is equal to $\left( \left( 60\times 3 \right)+5 \right)$ minutes as one hour is equal to $60$ minutes. $\left( \left( 60\times 3 \right)+5 \right)$ minutes means $185$ minutes. Thus,
$3$ hours $5$ minutes $-$ $45$ minutes
$=185$ minutes $-45$ minutes
$=140$ minutes
$140$ minutes upon dividing by $60$ gives $2$ as quotient and $20$ as remainder.
Therefore, we can conclude that $3$ hours $5$ minutes $-$ $45$ minutes is equal to $2$ hours $20$ minutes.
$\left( C \right)$ $10$ hours $35$ minutes is equal to $\left( \left( 60\times 10 \right)+35 \right)$ minutes as one hour is equal to $60$ minutes. $\left( \left( 60\times 10 \right)+35 \right)$ minutes means $635$ minutes. $1$ hours $55$ minutes is equal to $\left( \left( 60\times 1 \right)+55 \right)$ minutes which is equal to $115$ minutes. Thus,
$10$ hours $35$ minutes $-$ $1$ hours $55$ minutes
$=635$ minutes $-115$ minutes
$=520$ minutes
$520$ minutes upon dividing by $60$ gives $8$ as quotient and $40$ as remainder.
Therefore, we can conclude that $10$ hours $35$ minutes $-$ $1$ hours $55$ minutes is equal to $8$ hours $40$ minutes.
$\left( D \right)$ $4$ hours $20$ minutes is equal to $\left( \left( 60\times 4 \right)+20 \right)$ minutes as one hour is equal to $60$ minutes. $\left( \left( 60\times 4 \right)+20 \right)$ minutes means $260$ minutes. $3$ hours $40$ minutes is equal to $\left( \left( 60\times 3 \right)+40 \right)$ minutes which is equal to $220$ minutes. Thus,
$4$ hours $20$ minutes $-$ $3$ hours $40$ minutes
$=260$ minutes $-220$ minutes
$=40$ minutes
Therefore, we can conclude that $4$ hours $20$ minutes $-$ $3$ hours $40$ minutes is equal to $40$ minutes.

Note: We should be careful while converting one unit into another. In this problem, if there had been seconds, then we would have to convert all the units into seconds and then perform the operations. We should remember to convert the units back to the original form at last or, our final answer will become incomplete.